I've noted the issues you have, plus I've had trouble keeping weight off as I get older. I took a different approach to pack weight. I consider that my load should never exceed 25% of my ideal weight (50 pounds, given my 200 pound ideal weight.) I consider the excess weight part of my load. So, on a recent trip, 25 pounds of gear and food, and 20 pounds of excess weight meant that I was really carrying the equivalent of a 45 pound pack - and it felt about the same as when I was 35, not overweight, and carrying a 45 pound pack.

As far as the potential injury issues, I haven't increased my first aid load. Instead, I've started using two hiking poles instead of one for increased stability, walking a little more slowly and attentively, and being a little more cautious in my decision making (I might have crossed the stream on that log 20 years ago; now I scout around for a better crossing spot, or get my feet wet.)

I've also found that I'm not going into quite as remote areas as I used to. (I never went into truly remote country, but I did go to less well-traveled areas or at times of lower use.) Now, I tend to accept a more crowded trail as simply another safety valve - though I still tend to camp away from those crowds, by carrying water from the creekside valley campsites where they camp up to the next ridgetop, which I have all to myself.