Rat Feeder Question

Hi everyone!
I've started feeding my BP live because he stopped eating the frozen.
I got him a large fuzzy rat because it was a size that the woman at the pet store said wouldn't bite yet, however I know he can eat something a little larger.
I'm wondering if you guys can tell me at what size/age feeder rats start fighting if the snake doesn't grab it?
I'd like to know because my BP is jut starting out on live and is very gentle.

Live can be done safely IF you are responsible and knowledgeable, I have fed well over 20000 live preys without any incident so so have countless other people.

A few important points are

Feed an appropriate size prey.

Pre-scent the room by leaving the prey near the enclosure 1 hour prior to feeding.

Make sure the feeder since you buy them is well fed and well hydrated (offer food and water while pre-scenting the room)

Do not stun the feeder.

Do not stress the feeder.

Remove the feeder if uneaten within 10 min.

Generally speaking a well fed well hydrated, stress free feeder will simply fall asleep in a corner if not snatched soon as it is dropped in the enclosure.

There is no such a thing as a rat that will go and attack a snake if the snake ignore it if you do all that, horror stories and pictures always have a back story to them that does not reflect responsible live feeding.

All right, thanks so much, that's very helpful. The reason I asked was because my BP is very gentle, so thanks a lot!