I used to claim that I don't want to live past my fourties... now I can see myself as a Sex in the city chick (minus the heels). They done well in the later life too.

The thing is... that you change your priorities without even knowing it... "growing up" and maturing happens slowly, you mostly do not even realize it. And each age has it's specifics... good and bad.

And yes, you don't need to grow up. YOu stated you don't feel childish, so don't worry about that. Nobody is all wise and mature in their 40s nowadays.