Researchers reviewed 32 studies on activity and mood in people 65 and older. They found the combination of low-intensity aerobic exercises like walking and cycling plus strength training 3 days a week had people feeling much happier. Doing both can make you feel 10 to 15 years younger.
When you do start lifting weights, don't judge your progress by the scales since muscle tissue is heavier than fat tissue, so it might look like you are gaining weight. The best method to measure your progress is by the fit of your clothes. The fitter you get the larger your clothes will fit.
Also practice keeping you tongue up to the roof of your mouth a quarter of an inch behind your front teeth while you're lifting weights. You'll find you can lift more weight for more repetitions. A gentleman who attended one of my seminars where I taught that technique went back home and was able to bench press more than 500 pounds. (Not that 500 pounds should be your goal – it's not mine).