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.
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)