You are right in that the onset of Osgood Schlatters tends to be around age 10-12 years in girls. Osgood-Schlatters is a self limiting condition and usually gets better regardless of what action you take. HOWEVER..... Jumper's knee is not!! If you are suffering from Jumper's knee as opposed to Osgood Schlatters then you will need a considerable period of treatment and rehabilitation before your symptoms disappear. Treatment and rehabilitation for Jumper's knee (see advice below) won't do you any harm if you are suffering from Osgood-Schlatters.