I think your neighbour, at about 50, has been wrongly advised. Walking around, limping, is also compromising his quality of life.My neighbor is probably 20 years younger than I and the doctor told him to just put up with the knees as long as he could so he gets around with a bit of a limp at times but no plans for surgery.
For me at 70+ with no cartilage at all and an unstable knee, it's either compromise quality of life or replace it and get on with life without the ache or feeling like it's going to collapse when the bones shift.
50 is not too young to have a knee replacement, since the replacements can last 30+ years nowadays. I would advise him to seek a second opinion, from a surgeon who will consider the state of his knee and the impact that has on his quality of life, before he/she looks at his age.
New Zealand
My TKR did fix that problem, and I wonder if it would help you too. I'm finally back to walking 3X a week, a mile at a time, and even steep hills at times---no hamstring issues at all. I'm adding strength training back slowly too, but all the things that aggravated my hamstring tendons/muscles before the TKR are no longer an issue.