You have a very common problem. No, it's not too late, but you will need to change how you distribute treats.
It doesn't matter if you have very, very tame and friendly chickens or chickens that almost never get handled, if you hold out your hand with a bunch of tasty treats to a crowd of chickens, they will mob you, all trying to out-compete the others to get their share. This happens to the best of us. Fingers get bitten in the process. You might say they are "collateral casualties".
If you have a favorite chicken and you want to have a special treat giving moment, pick up that chicken and go someplace out of sight of the others to visit, cuddle them, and give treats. You will be surprised how calm and respectful a chicken can be if she doesn't think another chicken will beat her to the treat.
If you wish to treat the entire flock, it's best not even to try to deliver them one at a time to one chicken at a time. It flat out won't work. Just toss the treats. The way to make it more equitable for older chickens that can't compete as well as the younger ones is to toss treats for the young ones at one end of the run, and while they're occupied, give treats at the other end to the old and the slow.