The best exercise in the world won't benefit you if you don't do it. The one minute exercise takes very little time, space, or equipment but it has made me strong and limber. I hope it works as well for you.
Stand with your feet somewhat apart and a single weight on the floor just to the right of your right foot. Look at the weight throughout the exercise.
In one cycle the weight moves up on the right, then down across to the left, then up on the left, then down across to the right. When the number of cycles you are doing becomes easy, add one or two. When ten cycles become easy, go to a heavier weight. Exercising once a day is plenty.
The elderly often find it difficult to get up out of chairs, climb stairs, and pick things up off the floor, the one minute exercise strengthens those movements especially.
Extra fitness tip
If you use stairs frequently try going up them two at a time. At first it will seem awkward but after a while you will find that the strength in your legs is greatly increased. Soon it will seem slow and clumsy to go up stairs one at a time. This exercise takes less than zero time and effort since going up stairs two at a time is faster and less work than going up them one at a time.