婴儿、儿童、少年、成年 and other words related to age I'm looking for words to define grade levels from babies to adults.
According to what I've found on Baidu, the basic division is:  

(童年)
婴儿 - 0 to 3 years old
幼儿 - 3 to 6 years old

(少年)
启蒙 - 7 to 10 years old
逆反 - 11 to 14 years old
成长 - 15 to 17 years old

成年 - 18+ years old

But according to the dictionary, 启蒙 and 逆反 mean "to initiate" and "rebellious behavior", which doesn't seem to relate to age at all.

Are there better words to add up to 级 to define these grades?

Thank you
chinese characters related to age, there're three main sources.

the first one is 論語, chapter 為政

子曰：「吾十有五而志于學，三十而立，四十而不惑，五十而知天命，六十而耳順，七十而從心所欲，不踰矩。

that 

而立 - 30+

不惑 - 40+

知天命 - 50+

耳順 - 60+

the second one is 釋名, which was written in 漢 dynasty

in 卷三﹒釋長幼 (page 57-60):



"人始生曰嬰兒﹒胸前曰嬰"　嬰 - newborn, before breast (breastfeeding)

"兒始能行曰孺"　孺 - started to walk

"七年曰悼"　悼 - 7+

"毀齒曰齔"　齔 - losing baby teeth ( 9-12?)



"十五曰童"　童 - 15+

"二十曰弱"　弱 - 20+

"三十曰壯"　壯 - 30+

"四十曰強"　強 - 40+

"五十曰艾"　艾 - 50+

"六十曰耆"　耆 - 60+

"七十曰耄"　耄 - 70+

"八十曰耋"　耋 - 80+

"九十曰鮐背", "或曰黃耇", "或曰胡耇", "或曰凍梨", "或曰齯"　鮐背, 黃耇, 胡耇, 凍梨, 齯 - 90+



"百年曰期頤"　期頤 - 100+

the third one is 說文解字, also of 漢 dynasty, which was published earlier than 釋名. some explanations were different from 釋名, e.g. 耄 is 90+.

btw, talking about age, remember to consider "虛歲", or "虛齡"

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000111350

there're several more age related characters / words, have fun :)