First off Bambi is a Movie, yearling deer are called FAWNS!
As to your question, I can only comment on where I hunt but our Either-Sex Tags can be used on any deer the hunter chooses to harvest. On our Anterless Tags can only be used to harvest a Doe (female) or spring 04' Fawn. So it boils down to personal choice no rule on size or age. I personally do not shoot a fawn or a doe with fawns either but I also don't think it is wrong for someone else to choose to do so. If they are happy and use the meat from harvest then I am happy with them. Does it really make a difference if he shot a 55lb or 75lbs dressed deer? The point of hunting is to keep populations in check and with the land carrying capacity. This will also accomplish good herd health among the deer which included is a variety of age, sex and size of the species being harvested. So from a management perspective some young, some middle and some old harvested of both sexes in the species are a good thing and one might dare say even a goal(given the PC time we live in).
As far as him bragging, I could take that 2 ways.
#1-his first deer and he is truly excited. Further more with inexperience some can not tell the difference or know the difference until they get some experience or help from a veteran hunter.
#2-experienced and likes to brag about harvesting animals - unethical in my opinion and is desperate need of some direction from a true sportsman who not only hunts but love the animals in which he persues!!! (Like many of the fine members here
)
BTW you have every right to turn a deaf ear and I as a hunter respect others choice to do so. I would tell your co-worker your feelings and to refrain from involving you in the future.