I have a lot of interests that do match my age and a lot that don't. I'm 26 and I tend to listen to music that fits with many people in my age group, and I also watch a lot of current TV shows, what's going on in the news/politics to some extent, and I'm into fitness and health, I have a decent job, and I'm a full time student.
Younger interests/characteristics: I like games like animal crossing and playing on my DS in general, I love stuffed animals/toys and I watch a lot of cartoons. Adventure Time, Gravity Falls, Steven Universe, Over the Garden Wall, etc. Although I don't think it's that uncommon for ppl my age to like these cartoons really tbh. I like arts and crafts. I'm often easily amused. I can be a little naive about certain things someitmes I think.
I feel like our 20s are really weird, because you have young less mature (this isn't meant to be offensive) 20-somethings and then proper adult 20-somethings. You have people in their 20s who are living at home with their parents, going to school, maybe into partying, maybe more introverted and into gaming or their shows, etc. Then you have 20-somethings who've already started families and they're moms and dads already, then you have 20-somethings that are in a proper well-paying career already, with a much more adult-like vibe.
I have friends from all these categories. I don't believe one is better than the other, but it's definitely an interesting contrast between: Friend A: 24 years old and is dependent on his parents, plays a lot of games, goes to Wasteland Weekends, doesn't work, reads a lot of we comics and dyes his hair rainbowy colors; Friend B: 24 years old, graduated from a good school, her wardrobe consists of lots of expensive work clothes, works for a well known company, has a lot of high-end clients. Friend C: 23, had kids right out of high school, has to be responsible and think about things from a family point-of-view, everything involves their kids.
Anyway, cool question.