I'd certainly instruct if I could but at 57 years old there's no way I can justify the enormous expenditure in both time and effort to do the CPL exams.
A mere spring chicken yet!
I've just started a career as FI. I know one school where the CFI and deputy CFI are both well over 65 and still going strong.
You're right, it is a big effort, then you have to do the FI course which I found to be the hardest flying I've ever done, but I'm glad I made it.
TheOddOne