It appears that about 80% of those that died in China and Italy from COVID-19 were over 60-70. But for those that were younger, especially those in NY, it appears that obesity was one of the most common characteristics. This is likely related to insulin resistance that can be radically improved with diet strategies like Time Restricted Eating This new study in the journal Nutrients details precisely how exercise improves your immune system. There are many types of exercise but my absolute favorite is blood flow restricted training that I detail extensively in this article from earlier this year One of the reasons it is so useful is that BFR increases nitric oxide which is now being studied to treat COVID-19 at Harvard Medical School as reported in todays NY Times.
I have been exercising for over half a century and have never seen a strategy that improved overall metabolic and physical health as this strategy, especially in those over 60. You can use inexpensive $15 bands or treat yourself to the KAATSU system described in the article which you might be able to justify if your gym is on lockdown.