The only truly accurate way I’m aware of is to section the teeth and count growth rings. You can get pretty close by judging tooth wear but you have to be careful comparing to charts and photos as different browse will cause different wear. In the forest where I hunt whitetail they show excessive wear for their age, I’m assuming from eating woody browse more than farmland deer. A deer that was shot in the area I hunt was judged as an 8 1/2yr old going off a chart but from years of trail cam pics and previous years sheds from that buck I was about 90% sure he was only 6 1/2. If he was 8 1/2 then I’ve shot a lot of 8 1/2 yr old deer up there as well as several that would have to be 9 and 10 yr old, which isn’t very likely