I'm guessing it's a bit easier if you start as a kid. It's just what life is like to some degree. Still, can you imagine how much FOMO you would have, literally confined to a barrel? Puberty must have been extra weird for him.
I mean, to be direct about it, desire comes from the brain. The poor dude just didn't have a body to then be horny with. Also, genitals operate on a slightly different circuit, so they often can remain functional even if voluntary things have been knocked out.
Agreed on it probably being easier if it's something you're used to and not actively in pain.
Not everyone gets a lot of FOMO, so I could imagine that might also not be much, though.
I mean, maybe you just mean frustration/sadness that he can't do as much as other people, or to do specific things he wants to do. And I could imagine that could be just incredibly tough. Like all sorts of people with severe, debilitating conditions. But FOMO is kinda a different (more childish) thing than that.
Imagine if you find out that normal humans could breathe underwater, and there 100 billion people living underwater. Us 8 billion people unable to live underwater are the "iron lung kids".
The all say "imagine not being able to 'fly' underwater, or not riding a gigantic squid - I would kill myself to end my misery!"
What would you respond to that? I'd be like "eh, must be nice, but I've lived above water all my life. It makes no difference to me."
Literally the very beginning of the linked article:
Paul Alexander contracted polio in 1952 when he was six, leaving him paralysed from the neck down.
The disease left him unable to breathe independently, leading doctors to place him in the metal cylinder, where he would spend the rest of his life.
He later regained some very limited mobility, allowing him to leave the iron lung for very short periods; but I doubt that includes the fine motor control needed for a typical controller. You could possibly design something he could use to an extent, but it's certainly not as easy as just toss him in there with an xbox controller.