With no other information give up to the min raise on the flop. Depending on villain this could be a lot of different hands but it's usually one that beats you. I could be a 9X hand trying to inflate the pot or it could be a pocket pair finding out where they are. There are opponents who will min raise bluff but it's rare.
In any case fold on the river, you are counterfeited and most bluffs beat you at that point. There is an outside chance you are beating a low pair but that is it.
Fold river... you have 7 high. Given the exposed 9, I can be on board with calling the min-raise on the flop, although I'm wary of calling raises from old guys in general.
