You should be able to get 2 years, easily, out of a good string/cable set with average use and minimal upkeep. You don't need to add wax each time you maintain the string either, using a piece of masons line and burnishing a little just to heat it up will bring the wax out and give you a smooth string again. Just be sure to check for any foreign debris before sliding the line up and down the string (sand, dirt,etc.)
If you shoot leagues, a lot of 3d and then hunt with 1 bow with practice in between it may not hurt to consider swapping out every year, or you might just want to freshen up with some new color scheme and keep the old as a back-up set.
