I agree with Burke. I have graphite rods that are over 20yrs old and I don't notice any degradation in performance. I haven't noticed any set in the tips but I really haven't looked. There might be a problem if a rod was repeatedly over stressed by bending to excess but I don't know that.
If you follow the general guidelines given in this FAQ post
I think you will be fine with a used rod. The biggest problem you have to be careful about is impact damage. A rod with impact damage can break at the damaged location.