EDIT:After trying enough I was able to confirm that all of the three gold career achievements are unlockable, so the first two paragraphs of this guide can be ignored which is the disclaimer and the one after, I have nothing else to add to this guide because the info provided here is enough to get the achievements. I still stand for my point of wanting to receive more information in order to improve the guide, and another point is that the method of the Silverstone event is completely usable to get an easier gold medal.
Original solution:
DISCLAIMER: This is not a full guide that will guarantee you the achievement because as you can see no one achieved it so far, so this will be more close to a roadmap of what to do and don't but I think it is just a matter of time until someone gets it. And in case someone sees this and ends up trying to do this, comment below what did you find in your career because I don't think I found everyway to fail this achievement so any other tips will be helpful.
Something else to be pointed out is that according to some players it was possible reach a gold medal overall before but the achievement didn't popped, but according to the developers it was fixed after some time, and on PlayStation there are people with the corresponding trophy and because the game on console it's on the same version on both so getting the achievement is probably just a matter of time and patience.
Before I start explaining the events I also wanted to point that this is same for all three career types the short and the medium and the large one. Also some tips that were discovered so far that will be necessary to know before starting the career:
*Always choose the easy difficulty in all three careers, why? Well it's because you will make it easier for yourself against the AI obviously, and also the difficulty affects the the times required on the test events and some of them can be a little challenging even on easy so just choose it and don't worry about it.
*Playing offline is a good way to have a backup save if anything goes wrong, because in test events I had four different times where I lost my career after getting a gold medal but my overall one dropped to silver so I recommend using on the test events only because I didn't had problems with any races.
*DO NOT restart events with the option on the menu and always finish the events with gold medals on first try in order to not have to deal with bugs because I had a lot and according to some other players that tried this, say that the game registers your first result so if you get silver medal but restart and get a gold medal the game will drop you to overall silver so make sure you don't make this mistake.
*This is not a skill required achievement overall but this a racing sim so don't think this will be a simple Forza career because there will be some difficult parts for beginners so finish everything else in the game and after that you should try to do this one.
*About the overall medal, it needs to stay in gold throughout the entire career because if it goes down to silver it doesn't come back to gold again.
*There are only two types of events: the race ones and the test ones both will be almost the same in all of them in races there will always be training, qualifying and the races themselves, and the test ones will vary depending on the objective.
*You need to be the fastest in every event, every training, every qualifying, every test and every race you will need to win or get the fastest lap in order to get a gold medal in these sessions.
*Deleted laps doesn't matter, if you cut the track you will see that your time is red and that your lap will not count, but as long as you get the fastest lap or win the race it will not change anything on your medal.
*In races there will be two objectives that don't give points and are not necessary for the gold medal, which are the one for overtaking two adversaries and for having 100% of your laps being clean, the first one is impossible because you will start on first place so there is no way to overtake anyone even if you give them the position it will not count but both objectives doesn't matter so don't worry about them.
*Before the timer goes out in every race or test event make a save on the pause menu to make sure your game doesn't crash and make you lose some progress because I had this problem a lot of times so yeah better be prepared to such thing. And in case you save and the game crashes on the second try you should go to the pit or retreat to the garage through the option on the pause to menu to avoid this issue.
*Because some events need good results a tune could be needed to make it easier so this is a video just for that:
Credits to Blu3 Angels
In the events themselves I will tell when to look for a tune because it will not be necessary in every event.
After the debrief of everything let's start with the events now:
First test at Monza
This one will be after you start your career and it doesn't matter because it doesn't give any medal, it's only a way for the game to recommend you a difficulty based on your performance but as I said choose the easy difficulty to not make things harder for yourself.
Second and third test at Monza
Both are simple ones only requiring you to get the fastest lap but the 2nd will be on wet condition and the 3rd will be at night.
Before moving you will be able to pick a vehicle to drive during your career, for you to able to get tunes, the car to choose is the Porsche and is also considered the fastest car for the career so this is the one you should pick.
First race at Zolder
As it was mentioned before the three initial sessions which are the training and both qualify sessions just require for you the get the fastest lap. And there will be two races which also just require you to get first the place and you will be good. For all of the other races it will be the same process as in this one so use this as your usual procedure for all of the races in the career.
Fourth test at Brands Hatch
This is the first event that you will probably need a tune so use the video at the start of the guide in case you need it, now with that out of the way the challenge is to do 7 laps in less than 11:10 minutes if you are on easy difficulty, and for that you will need pace of 1:33s in your laps to get to this goal, there is also the opportunity to use the save after every lap to make you sure you don't make a mistake and lose it all.
And as it was mentioned before you can play this one offline to make sure your overall medal stays on gold after finishing the event, because there is no way of coming back after getting to the title screen while you are online.
Second race at Brands Hatch
Same procedure as always be the fastest in every session and win the races and you're going to be good.
Fifth test at Misano
This is an easy one with no clear goal other than testing your tires so just drive around doing slower laps and build your way up to faster laps to be the fastest. And be careful with the tyre temperature avoid curbs and don't push the car to it's limit it will only burn the tyres with high temperatures so careful with that as well.
Third race at Misano
Same procedure as the other two be the fastest every session and win both races to get the medal.
Fourth race at Hungaroring
Same procedure I guess you already know it by know.
Sixth test at Nurburgring
This is another easy test which only seems to require for you to get some consistent laps and you will be done.
Fifth race at Nurburgring
Last race of the first season but same as the other races before as you could have guessed it.
Seventh test at Paul Ricard
Once again just another test to go around without a objective to beat just make sure you improve your laps and make everything as usual to finish this one.
First endurance race at Monza
Only one race session with a longer time and more pit stops than the other ones but it's the same thing be the fastest and win the race to get this one done.
Second endurance race at Silverstone
Once again another race and once again the same procedure but we're getting close to the end at least.
Eighth test at Silverstone
Ok this one is not easy but there is a way out which I can't confirm if it works but first let me explain the challenge itself. Your objective is to get a time of 2:04:500 or lower on wet condition and based on online races I know that a lot of people can't get this time even on dry conditions so it's a pretty complicated one, but based on the video that I linked before it is possible but it won't be reachable for everyone even more for controller users. But thankfully I found an way to deal with the event which would be to wait on the screen of the event before going out on track and starting the timer, so this way the day time will go by and with the 10 minute clock stopped and as it goes the track will become dry and you could use dry tyres to get a faster time I managed to get a 2:02 but my overall medal went silver and I lost my career in this event. As people keep on trying and testing I will make sure to edit the guide in order to bring more info on random bugs and how to deal with events like these.
Third endurance race at Paul Ricard
Just as the other races this is the same, do the "procedure" and you will be fine.
Ninth and last test at Spa-Francorchamps
This is the final test and it will require for you to get a clean lap of less than 2:24, so if this sounds like a challenge to you use the tune on the video to make it a little easier.
Fourth endurance race at Spa-Francorchamps
This will be the longest one and will be the big patience challenge but it's the same as always be fastest and you're good.
Fifth and last endurance race at Barcelona
Yeah this is it the last one but nothing special is needed to be done, you do what you did the entire career and finish it once and for all.
If you followed everything correctly and was able to dodge all bugs and glitches congrats on the achievement.
If someone is able to finish one of three achievements for the career I would kindly ask to message me so I can improve the guide and be able to provide more info and in case I get the achievement first I will take out the disclaimer and confirm if the method on Silverstone works or add other miscellaneous info to complete the guide even more.
Either way make sure to comment if you think I should change something or add more to this guide I would appreciate it.