Peaked in high school and is still riding off of that into his 30's. He just wants to keep smoking pot and fucking his girlfriend while doing nothing of value with his life, like a lazy, arrogant teenager.
I doubt this was intentional, but Mogg to me is a twist on the stereotypical image of the NEET as an /r9k/-browsing neckbeard. By all accounts, Mogg was one of the cool, athletic "Chads" in high school, but he ends up being just as maladjusted and dead inside as any of those "blackpill" twats (he gloats about being on the dole as well, I recall). It's almost like a subversion of this idea that being superficially charming/handsome and being able to get with girls is enough to coast through life on.