I think its likely genetic & what they eat maybe but has nuthing to do with age. I got a little 3 point last year with dark chocalate colored antlers & doubt he was even 1&1/2 but he mighta been.
I dont know how personally but you can age them by their back teeth. Fella at the check station here does it for his own information. Me, I couldn't care less usually how old a deer I tag is. If I get a nice buck I'll ask the guy what he thinks, other than that I care more how much meat I get than how long its been around.