I want to send my little brother to bed early for farting at the dinner table.
Why do you want to send him to bed over that? Have you tried asking him to stop?
I've told him to stop a million times and he always does it in front of people
If your brother is continuously showing this bad behavior then it is okay to punish him for it. He will hopefully learn that it isn't right to do something so crass at the dinner table.
If I can't punish him, he's going to think he can do whatever he wants.
If he has gas it really isn't controllable. But if he keeps making sounds with his mouth by all means. If the gas it becoming a problem it might be good to take him to the doctor.