I really wanted to comment here, because I have had a very similar issue with DH.
Background is different. We met when he was 35, and I was 38. Both had quite a few sexual partners before (and me a long term marriage).
Sex was good at first, but not as frequent as I would have liked. Anyway, long story short, a few years ago the frequency because intolerable for me (once every 3 weeks, always at my instigation).
Unlike you, I couldn't keep quiet, and if I'm honest I was a bit of a nag. When he did perform it was amazing, but there were far too many time when he lost his erection (and this is why he would avoid sex : the pressure to perform).
It all came to a head (ahem) about 6 months ago, when I told him that if he didn't see a doctor, our marriage would likely be over. At this point, I was 48, and he was 45.
So, that's what he did. He had testosterone tests done, and all results were normal. This frustrated me, as I had hoped that he would get testosterone injections, and our problems would be solved. I think though, that a GP telling him that his testosterone levels were fine, actually gave him confidence. He bought viagra on-line. I co-incidentally had bought a rabbit, out of frustration.
Anyway, suddenly, we are have fantastic and very regular sex, 99% of which is instigated by him. He's only used the viagra once, and I've only used my rabbit once : for him, just knowing these back up plans are there if he loses an erection, has magically meant that he actually hasn't lost an erection since. This, in turn, has boosted his confidence, and he now wants sex alot.
Worth a try?