To get this achievement you need to have entered some exercise attributes in your Xbox Fitness profile, so that your performance can be compared to a similar group. Your fitness profile (bottom right on main menu) will then show a blue community bar on the right of your personal orange bar.
The only exercise attributes you need to enter for community comparison are gender and age. It appears that the height and weight information is only used for calculating calories burned.
The first time you use Xbox Fitness you are prompted to to enter privacy settings and exercise attributes (gender, height, age etc). If you need to enter or adjust these later click on the square in the top right corner of your screen to access the settings menu then scroll right to the exercise attributes section.
You will get this achievement when you beat the average community score in a drill challenge. The difficulty of getting the achievement is therefore based on your fitness in comparison to men/women in your age group. I got it in my first session after entering my age and gender, which came as a pleasant surprise.
If you don't pop this achievement quickly you have two options. One is to keep going until it unlocks as a natural result of getting better at the workouts. Alternately you can choose Secret Plan B and just tweak your exercise attributes to stack the deck in your favour e.g. by adding 20 years onto your age.