All the levels (rookie, pro, expert, etc.) keep track of is how long you've been playing the game, not your actual skill level. And this info is tracked on your save file (PS4) so if it becomes corrupted or you just delete it you will start back on rookie, so a rookie could actually have played an expert level number of hours.
Then as others have pointed out rank has nothing to do with your level. If a rookie starts playing ranked and gets to silver as a semi-pro you will get paired with them if you are an expert that is at same rank.