Does anyone know where I can find a good commentary for Cato Maior De Senectute?
I’ve used this one. It’s pretty good; I don’t know about the others. If you want to check your work against a translation (only do it when you’re either confident about your understanding or really and truly stumped) there’s the Loeb, which seems to be – baffling if it’s true – out of print based on an Amazon search. Some might discourage using a translation but you’ll likely make many mistakes you wouldn’t catch otherwise.
Ed: never mind; it’s just listed under its English title:
If you don’t mind reading on a screen or device this edition by Moore
https://archive.org/details/catomaiordesene00moorgoog
has notes on the same page below the text.
It’s downloadable as a pdf, of course.