Does anyone know the shelf-life of a golf ball?

A little old lady friend of mine who lives on a golf course goes out and picks up four/five balls a day, puts them in a box and gives them away. I got about six dozen, all slightly used, and up to six months plus old.

I was going to sort out the Pro-Vs, etc., and take the remainder to the range, but I don't know if it's worth keeping any of them(?)

Thanks in advance!