Harold, being Jewish, became an apprentice at the age of 13. Jewish tradition dictates that a boy can become an apprentice after turning 10-years-old.
Despite Harold being Jewish, he stole a ham which the Jewish tradition strongly forbids eating, which was most likely Harold's intentions. Also, while eating at the dinner table, Harold mentions prosciutto (a form of ham) and pork sausage, but they're not kosher. Rabbi Goldberg is even upset at Harold for stealing something that isn't Kosher in the first place. It's shown that Harold doesn't keep kosher. However, not all Jews follow the kashrut (Jewish dietary laws). As such, 20% of American Jews keep kosher.
When Harold's father tells Harold about the consequences of stealing / theft, you can go to prison for stealing, but Harold stole a ham which is a misdemeanor. Misdemeanors are minor crimes. Harold is also a minor. So, the consequences of him going to prison for stealing is very unlikely.
When Mr Green denies Harold for working in his store again after stealing a turkey, the turkey wasn't ruined like the ham was and Harold didn't have to pay back Mr Green for that theft. Which was probably the real reason why Mr Green denied Harold.
