@anon941368: Eh, 8 years divided in 2 groups of 4 doesn't seem like a good way for age groups, in my opinion.
I think they should be 9 years divided into 3 groups of 3.
Here's how I study human biology in age groups.
0-2 are baby/toddler years, the human brain basically can't remember anything, so those first years won't be memorable at all.
3-11 are the childhood years.
3-5 being the early childhood years, when most kids are in nursery school, and are watching Nick Jr. and Playhouse Disney.
6-8 being the core childhood years, when most kids are in early elementary school, and are watching Nickelodeon and CN.
9-11 being the later childhood years, when most kids are in late elementary school, and are getting into pop culture.
12-20 are the adolescent years.
12-14 being the early adolescent years, they still have many child aspects to them, but are starting to go through changes.
15-17 being the core adolescent years, they are maturing and starting to look like adults, but they still aren't legally adults.
18-20 being the later adolescent years, legally they are now considered adults, but biologically they're still adolescents.
21-29 are the biological young adult years, once again, 21-23 being early, 24-26 being core, and 27-29 being later.
30 is when real adulthood begins. 30-59 is just basically an adult.
60+ is an elder, but 60-something definitely isn't that old, you're not that old until at least 75, maybe even 80.