My father is 81. He still gets out bird hunting a few times a week, but I think that is more about getting out with the dog and staying active. He now keeps score with "birds he could have shot back in day", rather than actual birds shot.
For deer, he pretty much gave it up, other than the gun season. He bow hunted a fair amount until he couldn't draw his bow, then got a crossbow, but never liked it. The only reason he goes now is to hang out with the kids and grandkids. He hasn't shot his gun in probably 10yrs, and usually has some sort of excuse of why he didn't shoot a deer he saw. Honestly, though, I think he just enjoys watching them more than shooting them.
One of the sad things I've noticed over the years is that he is running out of hunting/fishing buddies. Only one or two are still hunting, and they really don't get around too well anymore.
As for younger hunters that have given it up, I just don't know that they were really into the hunting as much as the hanging out. Once life got busier, they didn't make time for it.