Your high school track days are over. Remember that as you consider how to maintain fitness after 60. Recovery is neither quick nor easy. So, rule number 1 is don't get injured. Rule number 2 is seek some professional input before starting to exercise again if you have been inactive. First stop is your doctor. No point dropping dead in the first week. 

Here is the recommendation for  a seven-day cycle: 6 days of activity, one day of rest from Dr. Stuart McGill is professor emeritus in Spine Biomechanics at the University of Waterloo. He's our age, these are his recommendation.  Check out his article on the CBC website. https://www.cbc.ca/life/wellness/how-to-change-your-fitness-routine-to-stay-strong-and-mobile-as-you-age-1.5471940

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Cycle 1: 

Day one: strength training
Day two: something else, like biking, walking, something to "get the old ticker going"
Day three: mobility training
Day four: something else
Day five: Strength training
Day six: rest
Day seven: mobility training

Cycle 2

Day one: Something else
Day two: strength training
Day three: something else
Day four: mobility training
Day five: rest
Day six: Strength training
Day seven: Something else

and so on

I’m going to try this new routine over the next six weeks and see what happens. 

David
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Assuming you can find the motivation to practice when the world is falling apart, I'd ramp up practice time slowly to avoid injury. Every year at jazz camp I meet so many "hobby" musicians who after 2 or 3 days are in trouble. Bleeding fingers on bass players, blown embouchures on brass players, tendentious flaring up in pianists and drummers. There are tears. 

So, I suggest ramping up practice about 10% a week. Warming up the muscles before you thrash the hell out of your instrument is helpful too. I'm working out in my home gym this morning and then heading to the practice studio.

For helpful advice I suggest all eager musicians read "The Musicians Way". I read it like many people read holy books. 

Good luck.

David