Prone Position Masturbation

I'm with a guy who has masturbated in the prone position since he was 10 years old. He had never used his hand until he learned he was masturbating "wrong". I read online about it and most sources say it's very unhealthy. I had never heard of it before he told me about it and he's been worried about having sex. He's been trying to use his hand more now, but he says it doesn't work as well and he needs to rub it against blankets or a bed. He had never had sex before while I have and he wanted to try and couldn't get hard enough to go inside me. He didn't realize that his low level of hardness wasn't as hard as it could get. I'm pretty sure him masturbating in the prone position has givin him some form of erectile dysfunction, neither of us know what we should do. Has anyone else every been with someone who masturbated like that? Or have any idea what to expect?

(like if it is ED or something else)