I am not a doctor.
But, it is my contention that arthritis is 90% genetic in nature.
I have had three knee surgeries, and now at age 40 have osteoarthritis in both knees. I used to play soccer and compete in judo, in additon to having a 495lb squat at a body weight of 215.
The doctors told me the same thing, that it was the sports I was playing and wear and tear that did it, but I have buds that did the same things, are the same age, and are fine. So, for my money, it is just bad genetic luck.
Even still, after feeling sorry for myself for about three years, I decided to get back to work. So, with a little help from glucosamine, fish oil, ibuprofen and a regular regimen of icing my knees every day, I'm back to squatting (405) and playing soccer twice a week. I am sore as hell afterwards, but I figure if the alternative is sitting around, I'll deal with the pain.
Long way of me saying to accept the condition if you truly have arthritis, find a way to work around it and manage it, and keep lifting if that's what you really want to do. The alternative that these doctors recommend - taking up swimming or golf or walking - is for guys in their 60's, not young guys.