The usual mn narrative of porn addiction and death grip in full swing I see. Reality is that as we age, penises lose sensitivity. Piv generally creates less physical stimulation than hand or mouth.
That's usually all there is to it, but also can be hormonal or psychological factors at play, performance anxiety being a big one, and that tends to be a downward spiral of self fulfilling prophecy. Whatever you do, do not let him know that it's an issue for you, certainly don't feel inadequate that you've not made him cum. Doing the opposite and telling him how much you're enjoying the sex may help relax him and reduce his anxiety. As daft as it might sound, if my dp tells me where or when to cum, that is often enough to get me over the edge when it doesn't seem to be happening. Another psychological issue for him may stem from the fear of unwanted pregnancy. Obviously unlikely to be an issue at your age, but there could be some mental scarring if he's been in that situation on his past.
Often if it's not working for us with night time sex, we'll stop and agree to 'finish off in the morning', and then it usually happens more easily. That's either down to tiredness, hormones (testosterone is highest first thing in the morning), or maybe simply sleeping with a semi all night in anticipation of the morning sex!
Alcohol can be another factor, even just one or two drinks. It doesn't prevent me from getting an erection, but I know it can cause me delayed ejaculaton. Which can be frustrating because it's a double edged sword when a few drinks helps relax and get me in the mood in the first place.
Going back to my first point, maybe try to reduce/minimise hand or oral stimulation on him during foreplay. Contrary to popular opinion I tend to find that more of that before piv tends to make the piv orgasm take longer, not shorter. Along the same lines, I find that the longer the foreplay goes on, the longer it takes me to orgasm myself. Sometimes (if you're both well in the mood) shortening the foreplay don't to very brief can help. But he needs to understand that then he'll likely need to carry on after his own orgasm to satisfy you properly, unless you're both in the mood for a quickie.
Finally, there may be some coupled toys worth trying together. Whilst men typically don't get off so much on vibration (in the way that women seem to), it can help provide a bit of extra sensation during piv. Either something like a wevibe for direct internal stimulation, or if you can handle a powerful vibrator on your clit the sensation can often be felt through into your vagina.