We all have different issues, but for what it's worth, my dad ran well into his eighties. He was an avid tennis player his whole adult life and developed some knee problems from that sport. To stay in shape for tennis, he ran - way before running was cool - way before the running shoe industry became such a thing as it is now. At the time, the medical practice was removal of the cartilages and therapy. He was about fifty when this happened, but he was determined to keep running. He developed his leg strength with a weighted boot of his own creation. (The man could rig anything up with duct-tape.) I don't even think running form was on his mind, but I also remember that he did change the way he ran, landing more on a bent knee, taking shorter strides. He completed a marathon with those doctored knees.

So anyway, part of it is "what you have", as SolaceEasy said; and part of it is that what you have might be able to keep working - with modifications.

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.