Thank you, Lorie. I've seen that before. I've also worked in an operating theatre. Even with only the medial compartment of your knee replaced, you still had the ends of your femur and tibia cut and shaped, to fit the prosthesis, which was cemented and hammered into place.
It is still major surgery. And you can't expect to bounce back quickly.
You know, here on BoneSmart, we have encountered a lot of younger people, some of whom have had PKRs and some of whom have had TKRs. With a few exceptions, who recover fast, the majority complain of being discouraged because they aren't progressing as fast as they had expected to.
Unfortunately, for recovery from a knee replacement, being younger does not give you any advantage. If anything, older people tend to have easier recoveries and feel less pain.