Well I am 66 and have a real problem now with my knees (no cartilage) and ankle (plate and 5 screws in that) with walking long distances.I actually think this is far more common than not taking hits at all. I've seen members of my own team take hits, walk back a few paces then come back in. I've tried both approaches, talking to them directly and having a word with a Marshall, neither seems to change the behaviour. They're usually rentals or players who seem to turn up for a few weeks in a row, never to be seen again.
I'd go mad if I tried Marshalling at my local site. They get a lot of rentals who dry fire in the safe zone, use their rifles to prop themselves up in the mud and instinctively lift their eye pro up to cooldown. Plus of course the lack of hit taking/not taking it properly. Not to say regulars never commit those fouls!
which is why I force myself to do airsoft for the exercise plus I love it wish I had discovered it earlier when I could run.
I do take my hits always but I do not walk all the way back to respawn as I would not survive a complete day, I walk back far enough to be well out of range and normally take a seat without my gun in hand and look for someone on my team that is killed and wait till they have been to respawn and have passed me on the way back in then I rejoin.