In the heat of the moment, a gentleman will remember to grasp her by the shoulders and not her head. This allows the man to suggest how deep he wants things, while she retains control over whether she gags or not. It sounds like the young gentlemen could be taught this courtesy.
Do it when he is laying on his back on a bed / sofa. It will be much harder for him to puch your head. perhaps he wants you to deep throat him or he likes to dominate. Just if you could talk openly with him about your prefrences and change it up to each other's prefrences everytime. That is the beauty about it.
Yeah OP, he's enjoying it but most guys that I know like it the deeper a girl can go, and some guys like to kind of "drive" even know you're the one giving the BJ. So don't take it as a bad sign
There's no normal. If you don't like it, tell him about it. If you like it, want it to go on, want to deepthroat, do it.