Stretch - Stretch - Stretch.
I am now 93 very active and enjoying life; river rafting - paragliding - zip lining - ice-caving - indoor rock-wall climbing - jumping rope... and constantly asked: What's your secret? If there's one thing I do pretty constantly it is stretching:
Routine: Ten sit-ups while still in bed, roll over and hold a plank position for count of sixty. Then do a dog and cat stretches, after which I swing my legs out of bed to the nearest wall and stretch as high as I can. Then - tightening my abdominal muscles - I slowly lower myself into squat-sitting, bounce up and down a bit and then slowly rise up again. Stand on one leg for a count of ten then switch to the other. Next I do hamstring stretches and shake my body real good to loosen up!
While my coffee is brewing I do my Microwave-hop, jump and dance and stretch, stretch, stretch :-)
I've found that doing this has strengthen my bones, improved my breathing, decreased stress on my joints. Hardly any fatigue, due to increased more efficient muscle performance.
For hand and eye coordination I like to juggle couple of balls. I read recently that squeezing those balls is good for lowering blood-pressure!