As well as cardio exercise which is great as Sqad has said, do gentle stretching exercises in the comfort and privacy of your own home.
Keeping flexible and supple is essential for mobility in later life and it makes life a hell of a lot easier if you can bend to tie your shoelaces, get out of your armchair without struggling and stretch to get to the back of the kitchen cupboards. Hopefully wards off aches and pains, too.
I love a cross trainer for cardio - works arms and legs and supports your hips, knees and ankles but is still weight bearing so is good for your bones.