I can't think of anyone in their 20s with whom I interact who don't use Spotify, personally. It's all I see amongst the younger colleagues at work. Of that age group outside of work, everyone's 'year in review' music summaries on social media are spotify-generated, and everyone who sends me 'hey check out this song' links are sending them for Spotify (with a few youtube videos I guess).
I'm sure there are people, don't get me wrong, but Spotify seems so ubiquitous amongst everyone I know who is in their 20s (even at arm's length) that I definitely believe my library of mp3s and player make me a product of my age and the odd one out.