when ppl wanna play and they ask for high lvls 35+ why do they do this? so they know the ppl are good or what?

Because if you play with people who are alot lower level, you will get paired up with lower level people, and the higher level guy has a very hard time leveling up

35+ isn't high level, high is typically 45+. But just because someone is low level doesn't mean they're bad, and having a high level doesn't mean you're good.

Depending on who's asking, it could be that they want to know you can play at a high level, or it could just be that they want to be able to find matches at their skill level. If you play people who are ranked significantly below you then you won't rank up as quickly.