I think 3.5 years old. I would have said 2.5, but you said there are no fields nearby. It has a belly, but the back has not begun to sag. It looks like a very healthy buck with not much in the genetic area. Should make a youth hunter very happy!
2.5 max and if not and he's really old, but judging by his body he is not, I would say he needs to go away and get culled as his genes are not what you want around if you want better deer in your area (better racks).