I want to try yelling at an old person.
Why are you going to yell at an elderly person?
The old person does not listen to me.
It's very disrespectful and wrong to yell at the elderly. You will come off looking like an elderly abuser and people will think you are a nasty person and don't want to be associated with you.
It's a good way to say my opinion.
I don't think it is, how would you feel if someone shouted their opinion at you? It comes off as rude and rash. If you want to get across to them, address them politely or try a written letter or text instead.