If you know anything about Dagestan, you know that they have more martial arts schools of all types there than almost anywhere else. And a very high % of boys of young age are going to be enrolled in these schools, as that is the tradition. In Caucasus, physical power and ability to stand for yourself is very important values for a man, so enrollment in martial arts for a boy is very common. And yes, wrestling is very popular, however so is kung fu, karate, sambo, muai thai, kickboxing etc. It's a misconception that all Dagestani's are wrestlers. MMA fighters from that region have a fist-hand, high-level source to practice and improve wrestling, but their first discipline won't necessarily be wrestling. Even in Khabib's camp, there are guys who developed striking first, before diving into mma/sambo.