There Are Other Factors...By the time I was about eight, people said that I was thirty. By the time a lot of people are thirty, I think that they just turned fourteen.
I think that experience, as well as attitude defines how emotionally, and mentally mature someone is. Just because you're fifty, it doesn't mean that you've experienced more than someone who is thirty.
I also think that once you are comfortable enough with yourself to not care if people see you as immature, then you're far and away more mature than the people who are self-conscious about it.