I've met a lot of guys who have really wrecked their bodies playing high school football. The amount of injuries that result in surgery from high school football boggle my mind. High school football coaches find it easier to tell you to "tough it out" or something similiar than to figure out how to best lessen your chance of injury, or ensure that any injury you have won't get worse through your playing (I really disliked the coaches at my high school. All of them (save maybe one of them, the one who actually played college ball and was drafted by carolina) have that really warped sense of manliness that you see in guys who want to remain jocks well into midlife despite the fact that they haven't played any real sports since they were your age).
Now, I know where most of that comes from. Let's be honest, most high school football coaches are ****heads whose concern for winning the game or "making men out of you" seems so supercede his concern for your safety and overall well-being (BE A MAN, they tell you).
With that being said, if football is your thing, I'd say go for it. But if you're not really that sold on the idea I'd say you'd likely be better off finding something else that you enjoy more. No sense in wrecking your knees for two fleeting years of football if you aren't gung ho.