SB - Shoot whatever make you happy. In a lot of areas - particularly areas that have a lot of vehicle traffic or areas that get pounded by hunters - a 2.5 or 3.5 year old deer is near the top of the age structure (due to hunting/poaching/motor vehicle collisions).

I know where I'm at, just taking a 2.5 year old every year is a task in and of itself. I'd say that Rob and Rybo can attest to that.

Due to whatever external factors, not every hunting area is conducive to growing 4, 5, or 6 year old bucks.

You know your own herd. Just ride around over the summer and take a good inventory of what's lurking. You'll know what makes a respectable buck for your area - once the season comes, you'll know a good buck when you see it. That's my best advice. If you want to increase the age structure, you might have to take a pass one season and hope he makes it to the next year without incident. That's my .02