Well, based on my experience I find it completely conceivable that 13-year-olds could be Zappa fans, but that's not what I was talking about.
As a 13-year old, sure I liked the music, but 13-year-olds aren't very discriminating. I liked lots of junk. What specially appealed to me then was the whole package: Zappa's snot-mustached contempt for everything filled a need for my burgeoning little rebellious brain; "subtlety" wasn't something I'd have learned to value in satire; the sexy parts obviously intrigued me; and I probably appreciated toilet humor more then than I do now.
At 13, I revered Zappa (even wrote him a fan letter) and would have hated the Velvet Underground if I'd heard them. Now the poles are reversed, a living illustration of how adults are wiser than 13-year-olds.
Would it be possible for me now as an adult to discount Zappa's personality and thematic preoccupations and just enjoy the music? Well, actually, I do still kinda like Hot Rats (too bad about that title, yuck) and "Watermelon in Easter Hay." Instrumentals, that is, and ones that groove a bit and could have been made by someone who didn't hate rock music. If I had Shut Up and Play Your Guitar, I might listen to it. But he sure doesn't make it easy to just isolate the music; even on my iPod copy of "Watermelon in Easter Hay" I had to edit out the obnoxious spoken intro. He was pretty determined to make us take the whole package, as even the ironic title of the guitar album demonstrates.