Your headcanon's as valid as mine! Like I said, I play pretty loose with it. Maybe instead of arriving in the city and working for a few years to build a nest egg, he left home with some money he'd saved, sunk it all into crypto, and then ten years later he's a burnt-out 30 year-old with more mileage on his body than most in his age group.
The important thing isn't really how old he was when he left, or how old he is now. What's important is that he left home young and full of fire, and years of hardship broke him down -- until he gets a second chance at life.
This is the same as when people get really hung up on the exact figure of his wealth. A lot of people obsess over it, like -- "Well, if he had $26,000,000 in crypto, after taxes, platform fees, and the devaluation of his meme coin as he exited with most of the liquidity, he'd really only have *wet fart sound!*" The exact number doesn't matter.
How rich is Guy? Wealthier than everyone he knows, except Carl Rhodenbarr.
How old is Guy? Appreciably older than Gabby, a bit older than Nicki, and roughly the same age as (or younger than) Madison.