To get this achievement you need to age up a sim.
This will happen automatically as you play through the game or can be done manually early close to the sim auto ageing up by baking a cake and adding candles and then blowing out the candles by the sim. You can check how long a sim has before they age up by checking the simology tab. (the picture of a head on the bottom right panel in game)
An issue i had with this is that my first age up was a baby ageing to a toddler, as this happened the achievement did not pop, but when i aged a young adult to an adult it popped, so i am not sure whether this was a glitch or ageing a baby to a toddler does not get the achievement, can somebody please confirm this so i can update the solution.
If you have any issues with this solution please comment before down voting and i will update the solution.