Richie says that Howard didn't let him go to Chicago alone until he was 19 years old. However, in the episode "A Sight for Sore Eyes," Richie was in Chicago alone, and he was probably 18.
Chachi: (to his boss) Look, I'm Sorry, Jake, but I gotta quit. You see, my cousin offered me this new opportunity: If I leave here, I get to live.
Al Molinaro does not appear in (at least) the syndicated version of this episode.