I'm twenty one years old and I just started quilting about...1-2 months ago. I really don't think it's an age thing - I think if you have a lot of time on your hands, you may be more inclined to quilt, although like someone else said, it's kind of something you make time for.
But being unemployed and having hours and hours of free time on my hands, I decided to dive into quilting. Boy am I glad I did! I haven't gotten any of the 'isn't that for older people' things yet, but the guy at the library did say 'aren't you supposed to quilt in the winter' when I picked up some quilting books awhile back, lol.