About -(으)ㅂ시다
Hello!
I'm studying the propositive sentence type and in my book it says that the formal polite -(으)ㅂ시다 should only be spoken to same age or younger people since it's improper ettiquete to say that to an older person/superior rank/elder.
My question is: how do I make a preposition to an older person then? And also, if you and your older friend use 반말 then you can just say it in informal plain, right?
Sorry if this is confusing... I am confused x.x
감사합니다