As a kid, I remember fearing growing up because grownups like to watch the news, which is boring.
A bit older, I feared having to work year round, and not get summer vacation.
Or look at all those commercials (e.g. 1, 2) for middle-age people reassuring themselves they'll never get old, never look old or slow down. (Or, heaven forbid, die.)
Personally, yes, I have become less into my job and more into my family and hobbies over time. I think that is common. But don't worry, nobody will force you to follow that pattern if you don't want to!
It is not people "refusing to act their age" that bothers me, if that's genuinely how they feel and what they want to do. Decide each day what you want to do and do it - and this should include goals and plans for accomplishing things in the future. But I am convinced that idle worry about who you will be, or what you will want in the future is just a waste of the present.