I don't think you're too old to work on cars. Just think of all the years of experience you have gained over the years that enables you to assess and troubleshoot things? I bet that making a new car payment would get really old for you, or anybody, very fast. The new car feeling goes away in about a year, but then you still have the same payment for 4 more years or so. Your cars are all paid for and you are very familiar with them. Even a new car might give you trouble and take time to fix, and the frustration would be greater because you would expect everything to be perfect. I thought a few years back that a new car was the way to go, but I missed timkering and that payment got old fast!
Good luck, I would stick with the ones you just fixed up.
Adam Bush