Babies 0 - 6 months since they can't really do much
Toddlers 1 - 3 years, old enough for daycare but not quite preschool or Pre-K if they still need to be potty-trained
Children 8 - 10 years; they appear to be more independent and be able to occupy themselves in a way that kids under about 7 may still have trouble doing, even in the age of technology.
Teens 15 - 17 years; high school but not quite immature enough to be 14/Freshmen. The only difference between them and YA since they nerfed the things that really made them different in the base game is that they're slimmer.
Young Adults 21 - 25 years seems like a fair representative time
Adults 40 - 45 years mostly based on the lines that appear on their faces
Elders 70+ given the way they walk, their posture and gray hair