I almost thing this is a runner having fun...but I will take the bait, particularly because I have a different opinion than the typical runner.
First off, I am very firmly now formulating the opinion that running causes no negative effects on the knees.
Other than having a built up heal and running harder down steep hills, negative effect on knees doesn't exist - caveat: perhpas if you have biomechanical issues...I am not a medical doctor....
I think...don't quote me, but I think Ball State University ...well some University's human performance lab discovered that runners had better knees that sendentary folks and even more so than occassional runners....when the knee is not prepared for running, it is not healthy to suddenly introduce running.
Runners have muscles and support tissue...well...supporting the knee of all things!
Anyway, I know all kinds of athletes who have never had surgery, who have had surgery and who have been duped into surgery.
Knees, back, neck, arm parts, etc etc....
Solution:
Run...and as much as you like. There is no limit to running, providing you are enjoying it.