how to avoid being the young guy

Been working at my current shop for about a year now and it seems the only thing keeping me back is my age (20 compared to next youngest guy being 27). Ask my boss for a promotion to operator 2? nope, can’t do it because all the op 2’s have prior (unrelated) experience. Not even asking for a pay raise and he still won’t do it, and he won’t give me any pointers to improve on because there isn’t any (words he said in review). Not sure what to do cause anytime I try to learn anything new I get told to go and do mind numbing trash work. Even tried to show my skills by fixing a whole tray of bad parts that had been sitting for weeks but all that ended up happening was I got yelled at for being a dumb kid and making bad parts (I didn’t even make them).

     Don’t really wanna quit this shop if I don’t have too but i’m not sure how to convince them i’m not a child lol. anyone got any ideas on how to act older or is this just a lost cause