I played D&D when I was in junior high and high school. But took a 15 year break. A few of my friends were playing so I joined a game and played again for a year, it was awesome.
I was deep into RC cars when I was about 12. But hadn't touched them since then. When I was 34 I got into RC planes and now FPV quads.
It's been really fun to revisit these earlier interests as an adult. For example I have the money now to buy the nice toys I wasn't able to when I was younger.
I also have two kids and am revisiting and picking up new interests as they grow up.
I'm in my late 30s now, but I'd say don't worry, there is always something new to be interested or excited by!
I've been with my wife since 1999, and I'm sure if either of us were the same as we were then we wouldn't be as excited to still be together.
Similarly the friends that I've lost touch with are those that _have_ stayed the same, and over time it's me that has no longer found this exciting or interesting in a person.
Personally, I think it is all good that we evolve and change. It keeps us from being stagnant.
Relative to worrying about no new areas to become interested in-- I was reminded of the Sharon Gannon quote “We create the world we live in. If we want to change what we don't like in the world, we must start by changing what we don't like about ourselves.”
I recently bought a new desktop with the intention of gaming again but for some reason I can't stand playing for more than twenty minutes.
According to Steam I have played two hours in three weeks which makes my new PC a poor investment.
I really want to enjoy gaming as I used to do but I simply can't, and I don't know whether I'm too busy or I've simply lost interest.