Nothing wrong with leaving him in the herd unless he's a bully and beating on the younger bucks with better scoring antlers. He does look quite a bit underweight for his age, however.
I've got one that is 7.5 years old this year. I've posted pics of him in the past... got hit by a car at 3.5 and crushed one side of his head in and blinded him in that eye. He only grows a half rack since then. We've had multiple chances to kill him over the years, but we all feel sorry for him and he's kinda one of our mascots.
I do have 2 other 6.5 y/o's that are culls this year that I will not hesitate to blast, one especially is a bully and notorious for breaking racks on other bucks, but we haven't seen him in daylight since he turned 4.5.