I often couldn't orgasm with a new partner (had the same partner for the last 15 years so no idea if it would still be an issue).
It's a pressure thing, I end up right on the edge but just couldn't tip myself over it, and then I'd end up flagging, the rhythm would go, and then there'd be no bloody chance. My first, (and usually second, and fifth) orgasms with a person would usually come from a handjob or blowjob etc.
Contrary to popular wisdom on here, death grip really isn't a thing. I'm far far more sensitive if I've been masturbating a lot, thus far more likely to go off on a hair trigger, rather than the opposite. Its far more likely that I can't get it up at all because I've had a recent wank than not being able to orgasm (Definately more of an issue now than 20 years ago)
Other causes of not being able to have an orgasm include:
Too much alcohol - A few too many beers and it's likely not to happen, likely linked to
Not a good match - If we can't get into a good rhythm together, then it ain't happening
Too much cycling - If I'm knackered, then it's a race between my orgasm and my stamina.
Too much lube - If my partner is extremely turned on, wetness goes up, friction goes down, and it can become an exercise in frustration.
My advice is to give him a really good handjob. Commit yourself to half an hour or so, go slow, tease him. Don't try and emulate "Death grip". I bet you'll get him there and then the pressures off for him in future.