From my own experience (as male) it has a lot to do with either age, amount of time be teen cllmaxs, or how excited he is.
If he young or inexperienced then he might not be able control his ejaculations. If the time between cllmaxs has been long then he will ejaculate faster. If he is really excited or turned on than that might be the cause.
Try having sex with him again after he has recovered from his ejaculation, i.e., when he is able to get hard again. If he is a sleep, you can gently wake him up by touching his erogenous zone.
There are things that can be done like having him think of something during sex that takes his mind away from the moment. He can practice muscle control when peeing. He can start and stop his pee several times while peeing. This is a good exercise. If his bladder is full during sex he will have a more difficult time with ejaculation.
Going to sleep afterwards is natural if he's tired as the release relaxes him, however it is not considerate. Try having sex with him earlier in the day or in the morning when you wake up. Talk to him about your needs with him.