Well, I'm 20 years old and have had three knee surgeries, all of them before the age of 16.
I've had two scopes and one major procedure...kinda why I'm going into medicine, go figure. Anyway, my last scope was Halloween my sophmore year of high school and it was just to clean up some scar tissue and excess cartiledge. I didn't actually have PT or use crutches after that surgery, but that could possibly be because I was young. But I was able to do basketball that winter, so I was basically only out of action for about three weeks. I waited too long for that surgery because I remember always having an aching knee and the day after surgery that ache was gone. So by all means, go for it!
But with my other two surgeries, that were to correct a dislocating knee cap, I was on crutches for both of those with a few months of PT each. My first was Dec. 30, 1999 and I was good to go for track that spring. My second, and major, one was Aug. 1, 2000 and I was able to play basketball that winter in November. It really all depends on the severity of the injury, the intensity of the procedure and the level of rehab you're able to start at.
Granted, we started fall softball last week and my knee swelled up to the size of a softball....it doesn't hurt. So I've probably got another surgery in my future someday, but thats what you get playing an additional four years of HS/college ball on an already shot knee.
Hope all goes well for ya!