I have a suggestion, but need to add a "warning label" to this posting.
Personally, maintaining isn't the problem, but libido is. I had a regular gal that had a higher drive than me and so I was trying various products.
I bought products on line and also at a health food store, but... the *best* product I found was (believe it or not) Ginseng tablets that I purchased at the dollar store. I could be at work and have a sexual thought and bam felt like a high school boy again (If you get my drift).
Here's the "warning label." Maybe it was a coincidence, but on three separate occasions, I found myself in combative situations with total (male) strangers. I don't believe that I initiated these, but who knows? And of course, it could be a coincidence.
I'm not the most passive person to begin with, but in my later years, such confrontations aren't common. And these three instances occurred within six weeks.
I still have a good supply, but now I only take these when I know I'm meeting a woman - rather than daily.