I very rarely masturbate. My boyfriend and I are pretty sexually active, and even when I don't have a boyfriend I am generally just too lazy to masturbate. My sex drive isn't nearly as high as it used to be in high school (in high school and college I did masturbate, probably only once a week though, as I've always been pretty lucky finding sex partners).
I didn't vote in the poll though, as I am over the age of 20, so I didn't not want to skew your results.
I didn't masturbate much as a teen, I didn't find it very enjoyable. I tried it a few times but did not find is sexually pleasing.
And not just the teenage generation, but the adult generation.
Well I'm 24, and I masturbate (albeit very rarely). My boyfriend is 25, and he masturbates about once a week.
I'd say many adults masturbate, but a lot of them also may have regular sex partners, so they may not have as much of a need or desire as teens. Plus when you get older your desires change. Work becomes important, and with that you have less free time, so the little free time you have you don't always want to spend touching yourself. Plus due to hormones not raging so much your desire for sex in general may vary from when you're younger.
So, yea, I think most adults masturbate, but not as often as it seems most teens do.