Without involving the word "school" how do you categorize the different age groups?

Pre-pubescent, pubescent, post-pubescent

Grades 1–6, (elementary)
grades 7, 8, 9/freshman (middle)
sophomore, junior, senior. (upper)
First grader, second grader, third grader, fourth grader, fifth grader, sixth grader.

Infant, baby, toddler, child, tween, teen, adolescent, young adult.

I agree with @zenvelo, except that I think that adolescent and young adult are one and the same.

Actually, make that teen, adolescent and young adult.

@elbanditoroso Which term goes with which age group?
@kritiper What if no mention of school related terms?
@zenvelo When does an infant become a baby? Isn’t “child” a general term as in “I have 3 children all adults now.” or “I have a 2 yr.old chid.”
@Adagio I don’t have a follow up question. Thank you all

Puberty isn’t directly tied to age, @flo. Puberty refers to physical (and usually mental and emotional) stages of growth.

Examples:

- prepubescent = girls who have not started menstruation and not started growing breasts (and other things besides)

- pubescent = starting to grow breasts and pubic hair, starting to ovulate, onset of menstruation, etc.

- post-pubescent = essentially a young adult.

For some, puberty begins at age 8–9 and ends at age 12 or so; for others, it doesn’t begin until 11 or later.

Puberty is a developmental stage, not an exact measurement.

(similar steps for boys: beginning to grow facial and pubic hair, lowering of voice, broadening of the body. And for both sexes, growth spurts to adult height.

Newborn, infant, crawler, toddler, walker, little girl/boy, girl/boy. Then, see @elbanditoroso

I would categorize them more on their mentality. I wouldn’t be able to give my opinion to total accuracy, rather being an estimation of what I would imagine to be my in-case mindset.

For the range of newlyborn and those unable to make much of their own decisions on a larger scale of what to or not to do, I would consider babies.
Once they become coherent enough to carry out a conversation with their own complex ideas, regardless of how much sense or explanation they give, I would consider them children, and describe them as young and innocent.
During the years of finding themselves and gaining the ability to master certain aspects of their character, they would be Kids, that or tweens.
In any aspect, once you become responsible for your own decisions despite if you are still underage or not, and having to learn, accept, and build on those consequences whether negative or positive would be when I begin veiwing you as a Teen or Young Adult.
Typically, there is a gray area in the 17–23 age range where some are more future aware than others, who are typically present-oriented and tend to make every day their very own drama packed sit-com. For those whose age would suggest adulthood, but attitude suggest otherwise, I’m typically more inclined to view them as an adolescent still, as their character choice resembles that of a teen.
Above that, you have your Adults. This is a range that is best separated in terms of proper titles. When speaking to a young woman who is no longer an adolescent you would typically say “Miss”, whereas someone older would generally be addressed as “madam”, or “ma’am” for short.

@Chocobunni I was looking for a list from experts similar to the ones in the link I posted,, for filling out a form etc., puurposes. But nice to see that you put thought into it.
When do we not refer to a female a young lady, a woman, and not a girl by the way?