It really depends on what age you are talking about.
For example, if we are talking about four year olds, there are lots of advantages and disadvantages to that age.
Lots of play time.
Lack of responsibility in most areas of life
Life is much simpler.
Frequent napping (I appreciate the ability to do this as I get older)
and a host of other things
Everything is at the whim of others.
Don't get to make decisions that impact you life in major ways.
Being oblivious to certain things in the adult world that could put you in harms way.
Being 14 is much different, as is 24, or 34, or 54. As time wears on, we gain more knowledge and experience. It is what we do with that knowledge and experience that shows maturity and shapes the future to some extent. Remember, at a very young age, the future of our lives is shaped by others. We must go to school, to teach us the habit of being in one place for about 8 hours each day (like a job). As we get older, we gain opportunities to do what we want, when we want. From vacations, to retirement.