Why or when do we say that someone is mature or immature? How do we define maturity?

I got the following definition off www.dictionary.com.

mature adj 1: characteristic of maturity; "mature for her age" [ant: immature] 2: fully considered and perfected; "mature plans" [syn: matured] 3: having reached full natural growth or development; "a mature cell" [ant: immature] 4: fully developed or matured and ready to be eaten or used; "ripe peaches"; "full-bodies mature wines" [syn: ripe] [ant: green] 5: (of birds) having developed feathers or plumage; often used in combination [syn: fledged] [ant: unfledged] v 1: develop and reach maturity; undergo maturation; "He matured fast"; "The child grew fast" [syn: maturate, grow] 2: grow old or older; "She aged gracefully" [syn: age, maturate]

oops! will be back. boss is around the vicinity. must act busy.