There are many variables involved. My best guess (since my wines don't seem to last long) would be a couple years at best. It would depend upon the acid level, sulfite content. Temperature, tannin, darkness, alcohol content kind of fruit.
Reds will last longer than whites, then fruit wines. All wines will improve with age then peak, then begin their decline. It wouldn't be a sudden drop but as you drink them you will start to taste the change.