But I think it's not that difficult these days to date Thai girls..it really depends on what type of Thai girls you want to date. If you are 35 and you want to date someone that work in the similar work field and she's 26, I think it looks ok. If you are 75 and want to date someone that's 20..hum, something strange is going on. I mean, the intention of both party.
Anyway! There's no strict rule as to the age zone. If you guys are really in love, who cares? :)