Nature

 Everyone has a stabilized mix of high or low levels of each ego state, and that determines what people refer to as his/her "nature" or normal interface levels. In a person who has taken a lot of beating or made lot of adjustments in life and seems withdrawn, both his Control Parent and Child Ego States would have become very low. Such a person would be more submissive, lack drive and enthusiasm in life. But Adult, Nurturing Parent and Little Professor Ego States may be high in such people. Old teachers, Nurses, Rural Farmers and Secretaries are examples of such an Ego State development.

This personality would not come across as a necessarily mature one, albeit it is definitely a "serious" one. At the same time, we cannot classify a generally bubbly personality as lacking in maturity.

Maturity is more portrayed, like I said by attitudes, thought cycles, decisions in life, compromises and adjustments you make or don't make general concern or the lack of it, general understanding of life and its priorities, and ALSO in interface with people. Maturity, also, like the Ego Mix is a function of life's experiences and bringing up in the formative years.

Thus, as opposed to those senior teachers, etc, a 10-year old tea-stall helper boy would have seen the nitty-gritty’s of life more closely and has a better understanding of life and its ways than your average college going teeny-bopper, who has hardly met with any of life's wiggeries.

And since experience and nurturing doesn't have rules of what stage you come across in life, maturity has nothing to do with age. But more generally, since life's experiences are normally seen to begin coming in from a certain age onwards, this is the popular notion.