老奶 and 老爸 is improper.
老奶 is not used at all. It should be 老奶奶(for elder female, typically old enough to be a grandma, because 奶奶 means grandma).
老爸 is usually refering to your father, I think it work as "old man", when talking about someone with no relationship, maybe 大叔 is better.
note: 爸 typically means father, only in some dialect it also means father's brother.
example:
二爸 means father's brother(2nd eldest)
四爸 means father's brother(4th eldest)
but you can ignore this, in official mandarin this is not used.
a simple list:
male:大哥(whose age like your brother's), 大叔(whose age like your father's), 大爷(whose age like your grandpa's)
female:大姐(whose age like your sister's), 大婶/阿姨(whose age like your mother's),大妈/大娘(whose age like your grandma's)