Whirls, I had no idea you were that old. Kudos!!
Sundaydriver. Why don't you take a look at the CRI rating. You can do it without a CPL or the CPL exams (but must have CPL level knowledge). It can be added to a PPL and will allow you to do everything but ab initio. Licence renewals, tail wheel, complex etc. Add an IRI to it and you can teach IMC.
On a PPL unpaid, but at your time of life I would imagine the flying would be the reward. However there are ways of LEGALLY getting payment as well if you had to go that route.
Flying schools are crying out for Instructors that are not going to up and leave for the airlines in a couple of months and the CRI can do a huge amount of the normal flying school work.