Five minutes headstand everyday does that for me.Facelift.
I would put it the other way round. Mix with people younger and fitter. So long as you can keep up reasonably their superior fitness rubs off. Much of my "sporting" life I have mixed with everything from teenagers [ who bounce when they fall off their bikes] to those about my own age. It also gives a younger outlook on life in general.Surround yourself with older, less fit people?
Medics sometimes express mild surprise that at the age of 63 I'm not taking any permanent medication.