How do 18/19 year olds have £100,000+ saved?

I’m 22 and I only have £0 in my spending acc and £120 debt in my credit card to my name, this guy I know showed us his bank account and he had £100,000 saved, it’s been a couple of years now so he’s definitely doubled or even tripled that now.

I looked in some other people that age have around that much money saved but how? This guy was a student at university btw, he’s my age.