Hasn't been with anybody in about 20 years? That means he's probably developed 20 years' worth of particular masturbation habits that you, unfortunately, are not going to be able to match on the first night.
I suspect that since it didn't work the first time, it might take a few tries before things are back on track for him. You'd think it'd be like riding a bike, but if he's developed any particular habits that sex with a partner can't mimic, then it could take a bit of practice. And there doesn't have to be anything wrong with practice