Well he's not some fat balding drunken westerner so he certainly won't need to visit the bars on Soi Bangla to get laid. Therefore the need for penicillin and herpes cream probably won't be needed. Nor will be the need to buy his entertainment.
My son is twenty one and and spent 8 months last year travelling with friends around Thailand Seems he rarely had a night without "company" with lots of memory photos of the numerous, very attractive girls he spent some time with. Some Thais and many other nationalities on their gap years, including Italian, Swedish, American and French. One of his friends hooked up with a Japanese girl and ended up back in Tokyo with her!
As the father of my 21 year old son, am I jealous? You bet I am!!!!!