As we get older we cannot expect our bodies to react the way they did in our youth. Our fitness efforts have to concentrate on maintaining strength, co-ordination, flexibility, and endurance. The normal course for our bodies is to loose muscle mass and gain weight starting in our late 40s to mid 50s. If you are over 50 forget the no pain no gain exercise ideas you heard as a youth. Your body is no longer young, has had many decades of pain and healing, and is losing its healing ability a little more each year.
Keeping your weight down is important, but not the only aspect of keeping fit. Getting my weight down got my blood pressure under control and I am convinced that is why I'm still alive. At 6' 1" it really does not matter much if I'm 190 lbs. or 200 lbs. What matters is that I stay active. No matter how much I train, work out, or diet I will never be able to attain the fitness level and strength I had in my late 20s and early 30s.
If I had put in the time and effort in my 20s to fitness that I do now that I'm in my 60s I would have been a beast. But when I was in my 20s I was not patient enough to go about a slow low intensity training program. Back in my youth a hour five times a week kept me in pretty good shape. Now I do two to three hours five to seven times a week. That's why I get up early in the morning. Just my thoughts.