You find yourself interested in and actively pursuing activites that exercise the other functions as you grow older. It's like you get bored with the stuff you always did before and naturally find different stuff to do.
Heh, actually I think the opposite is true for me. I have more life experiences that have taken the place of spending much time imagining possibilities. It doesn't mean I've lost my imagination, but I think a lot more of my brain space is used for memory storage these days.
I am a young-at-heart J. And I think I have gone in stages. A good amount of N as a child, a major S in high school and college, and more balanced now. In fact, many people on here type me as ENFJ or ENTJ. I am a definite ExxJ, with a pretty good balance on S/N and F/T.
Who wants to try a bottle of merc's "Extroversion Olive Oil?"