Purchased Hoyt Havoc in 2000, shot like crazy the first couple years, then since I shoot just a handful of arrows periodically throughout year (3 kids in last 5 years:d ). I've waxed this string once a year and there is no fraying...don't see me ever getting rid of this bow as it's "like riding a bike" anytime I shoot it. How long can a string make it?
I have always heard and been told, a string should be replaced no less than every two years. But, use of the bow determines how long a string can REALLY last. I would say, since the bow is 9 years old, go ahead and replace the strings/cables. Over time your strings/cables will stretch, leaving you with a bow that won't shoot as well as it could with proper string/cable lengths. Granted, if the strings creep/stretch, you can get them back into spec with twisting, untwisting strings/cables, but at this point, you should really just go ahead and replace the strings/cables. You should also be waxing the string moreso than once a year, even with a limited shooting schedule. In your situation, I would wax the string after you shoot to help keep the new string in the best shape possible.
I agree w/ Bols on how long the string should last give or take a little while considering amount of use. I wax my bowstring about every other time I shoot, and if I don't shoot for a while I still pull it out and put another coat of wax on.
Like has been said already, I've always been told the strings should be changed at least every 2 years. Of course, string wear can also depend on how much the bow is being shot, how often its been waxed (I know I wax every single time I shoot which may be over doing it but it sure has kept my string in good shape for a long time) and if there is any wear and tear from being in the field.