I noticed a huge difference in the toughness of the meat when me and my wife finished off the roasts from last year's button buck and started using roasts from my dad's buck (which was at least 4 years old). I didn't change anything in my slow cooker roast recipe, but man, even in a slow cooker those mature bucks just aren't as tender. It's as though their fat is just tougher and less buttery.
If I see a spike or doe in two weeks, I'm taking it. Tastes better the rest of the year.