I score antlers "on the hoof" as follows...
1. Hey! A deer. Is it a buck or a doe?
2. It's a deer....a BUCK deer.
3. WHOA!!!! Nice buck!!!!
4. HOLY $%&&*%$@#!!!! OMG!!!!
The one in your pic would be a #3 in my book.
Age? The only sure was is to check the wear of the tooth enamel on the molars. Most of us have to kill them first to do that because we just don't have the skills to get them to stand still long enough much less have them let us look in their mouths.
Buuuut......................If it were an Illinois deer (from farm country and not the suburban Chicago forest preserves) I'd gues that he was at least 2 1/2, but not more than 4 1/2.