I am 56 years old and retired. I lift weights 5 days a week and practice martial arts and a combination of jogging / fast walking 4-5 days a week. That being said I admit that I have had to scale down those things a couple of notches as I aged. But you can still exercise no matter what your age or health. Just take it slow and easy at first until you see what your limits are. I promise that not only will your strength / stamina improve but you will generally feel better physically and mentally.
Start out lifting light weights and build up. Take walks for 15-20 minutes and walk just fast enough to get your heart / breathing rate above normal. Work up to 30 minutes. These will build up both your muscular strength and stamina.