I agree with the simple fact that you should only harvest older deer, but I also want to point out that there are other factors that need to also be considered (genetics, food, hard winters, etc...).
You can improve the herd a lot by planting food plots for the winter months. You can also help the genetics by maintaining a good doe to buck ratio, which will keep the inferior bucks from breeding as many does and allow the dominant buck with the better genetics to do most of the breeding.
Again, I agree with letting the bucks get old enough before shooting them. I would rather shoot a doe with my bow than an imature buck during any season.
Thanks, HJ