I've decided to open both games to see how the two fared when creating Sims which accurately represent the age group they are a part of. For this comparison, I decided to use beards on the males to really test the games. I'm skipping over YA.
I think TS2 is the clear winner of accurately representing each age group. I'm personally not a fan of the age transitions in TS4, and this comparison highlights why. Teens don't look accurate, adults (not YA) look too old to the point where its exaggerated, and elders look far too exaggerated and old.
The Sims 2
The Sims 4