Hi Tony, I don't think anybody can say 100% how old a deer is but take into account where he lives, food sources and nutrition and total herd health and you can get pretty good at it.

Here is a link that really helped me to "get to know" how old deer are on the hoof. It's off the tecomate website. Say what you want about their shows, but there is some good info on the site.

http://http://www.tecomate.com/resources/articles/age-and-aging.cfm

Also: some of the other management minutes are pretty cool to read.