I would think the older an animal gets the tougher, and stringier the meat would get. Think about how an older person looks vs. a younger one, in relation to muscle mass, body tone, etc.

As far as age, I think a deer that has been in this world less time than an older one, would have less exposure to the toxins found in our environment, and probably be better for you and better tasting by default. All of the state hunting guides I have read so far for the states I have had the pleasure of hunting in, tell you not to eat the heart and liver of older deer, and to limit consumption of all organ meats to less than 1 pound per month, or some variation of that. Seems the heavy metals mercury cadmium etc., build up in the organs, as they are designed to do. Liver, kidneys etc., are just that, filters. What ever gets missed, ends up in the flesh and fat of the animals.

That said, I think any deer that is dressed and cooled quickly and aged properly will taste very good. The aging issue has been kicked around before, but I believe the university of Georgia did an exhaustive survey/experiment and they found that venison should be aged for ten days at 40 degrees farenheit to produce the best tasting flesh. There was a table in there also that explained as the temperature went up or down, length of time increased/ decresaed due to the slowing/speeding up of the bacterial breakdown process. Beef is typically aged 28 days at 38 degrees I believe, so something is different about the animals and the process.