If you have a choice, a yearling usually makes fine eating. Fine grained, lighter in colour, not too gamey in flavour and more than likely very tender.
However any animal in good condition will be good eating, even an old bull, if he has a good layer of fat over his back, chances are the meat will be tender.
Poor condition and stress results in gamey and tough meat, age isn' t necessarily the reason the meat is tough or gamey.
Hang your meat in a chiller for a week, keep it dry.

Good luck with your hunt.