I am 23 and I still have way too much imagination. Since I was a kid, I created my own inner world and my alter ego in my head. Of course, everything in this inner world (places, characters) grew up with me. I always found it weird to have all this imagination at my age, and I always fear that if people find out, they'll think I am ret*d or something. But I think that imagination helps me deal with the overwhelming reality that is around me, so I don't wish it would stop.
Also, I have an inner child and although I can be very mature at times, I really like doing kid stuff. I actually play a lot with children, and find easier to talk to them (and to people much older than me too). My favorite thing to do with kids is swings and spinning in circles.
There is nothing wrong with imagination, I think that people who don't have imagination have a rather sad life.