I am 30 years old and have been through 5 knee operations (all on my left knee). At 21 yeras, I blew out my ACL and ripped up the meniscus REAL bad when I was vert. skating. The Doc rebuilt it with a graft from my patella tendon. 11 months later, I ripped out the graft and destroyed more cartilegde (skating again). That time my knee was re-built using a graft from my hamstring. This ACL graft has been bomber, it feels solid. I have had two additional scopes to repair and cleanup scarring and meniscus frays. The last surgery I had, involved stem cells coagulatting on a specially prepared boney surface in my knee joint. These cells grew into to "new" fiberous cartiledge and my knee has been great since.
I would give up running if I were you. I didn't, although it took a few years, I certainly sped up the aging process by being stubborn. I now cycle and have zero knee pain.
I also quit skateboarding.
I would totally focus on building your quads. and hamstrings. These muscles support the knee and reduce the stress on the joint.
I lost about 20 lbs., this helps too: less weight to support, less stress on the joint
PM me if you want more detail on my ACL experiences.