Matchmaking hello?

Can someone explain how does a lvl 26 get into a match with people that are plat/diamond ???

This is not the first time i've got a game ruined by someone that is clearly a really new player and he's matched against people playing the game for years now, its not good beginner experience and it frustrates older players having a person on the team that we presume is inting and trolling but he's just started the game last week.

Riot plz