I just wanted to clarify something for other posters.
The OP says he put HD hand 'lightly on her neck'. This is very different to hands around the neck.
It doesn't do anything for me but some women like it. I don't like that but do like certain aspects of 'rough sex'. I had sex with a friend last summer and he also put his hand 'lightly on my neck'. He hadn't previously asked for consent because I don't think you can ask for explicit consent in every aspect of sex! But when this man did it, I shook my head and said no. He removed his hand immediately and, afterwards, apologised and said he wasn't sure and thought I'd might like it because of the other 'rougher' stuff I do like. I said I didn't like that, he apologised again and we had sex on another couple of occasions amd he didn't do it once.
To me, that is how consent actually works during sex. Someone tries something and then reacts appropriately to the other's response to it.
If the OP didn't feel threatened by it because of his reaction, then it isn't a red flag. That it indicates a lot of porn use might be relevant but that's a separate issue.
Honestly, some people on here give the impression that they have detailed conversations before sex about what is and isn't off limits. And maybe some do. But not everyone does and not every one feels it's necessary.
Tbh, OP, as for the ED, I would talk to him about it. A lot of men are embarrassed by it but I find that how you approach it makes all the difference. If he's found a position that works for him, he might think you're happy to go along with thar unless you say something. As others have said, sex is something you do with someone not something done to you (or it should be!) And you should be able to talk about aspects of it between times.
My boyfriend is 58. Sometimes he's fine, sometimes it happens. He's said that sometimes it'll last for ages and sometimes he can feel that if he doesn't actually have sex right now then he's going to lose it. I'm never left to miss out though. We talk about it and it's fine.
And it's a fallacy that ED in younger men is always down to porn and death grip. I'm not going to deny that that can be an issue but it can also be down to confidence, nerves, it having happened previously after too much alcohol and fearing it'll happen again even when sober and expectations/experiences/reactions from previous sexual partners.
I have a friend who has had ED issues for about 15 years since his early 40s. It happened once because of medication and then the fear of it happening meant it happened all the time. He can stay hard for 'other stuff' just not piv. He's never used porn. Hes had his hormone levels/physical health checked. He's been told it's psychological. And, yes, we do clearly overshare 🤣