Sounds like low testosterone to me.
I'm 63 and I was feeling the same way and my doctor said my testosterone was low so I been getting shots. Actually, I been giving myself shots so I don't have to go to the doctor every 3 weeks. Now, I'm back out there at every opportunity. I don't want to slow down except maybe after a succesful moment (in the field or in bed
) to take the time to enjoy and relish what I just did. I think that's the quality of getting older, being able to do what you use to and have the smarts to enjoy it to the utmost.
I don't hunt bad weather like I use to and sometimes I only hunt the mornings or the afternoons, not both, and I don't have to go ugly early anymore just to insure I satisfy that end of the equation.
Anyhow, do what makes you happy.