How old is the homeless dude? Is there a major age gap?

I think he's around 22-24 years old

With a highschooler? Weird

he's between 18-20(ish) is what his character chart thingy in the officials said. idk why they gave a range but that's the number

wait where’s the official chart

probably because they murked his parents, trafficked him to japan, and he was unsure how old he was then. Maybe they settled with an age but he could actually be older or younger within that range.