it varies depending where you are but around here they shed their velvet in aug/sept, rut is in Nov/Dec and they lose their horns in Jan/Feb.....thats usually can vary some based on individuals, ive seen bucks with hard horns in March and velvet in October, individuals though seem to loose them about the same time every year within a week or so....
rack size does not equal age, my wifes buck was a young one, prolly bout 3 years old, but have seen smaller racks on older individuals, biggest horns usually appear somewhere between 4 and 7 years depending on the genetics of an individual and they usually start to get smaller after that......some deer just dont have the genetic makeup for huge racks no matter how pampered they are.....genetics control the shape of a rack to a large extent but injuries can influence the shape to, even injuries no where near the head.....
general shape depends on species which is why for typical racks from bucks atleast a couple years old you can glance at them and say its a mule deer or whitetail......whitetails usually have a main beam with single points growing off it, mule deer horns like to fork.....
when watching deer its pretty easy to tell what bucks are young or old even if its early spring and they arent showing much for horns by looking at the nose, back and belly.......old deer have sagging backs and bellies and a roman nose......