Orr Family of Northern Ireland

Robert Orr was in colonial Pennsylvania in 1768 as he had a son born and christened in Philadelphia.  Family history says Orrs were Scots who went to Northern Ireland,.  Hoping to determine parents of Robert and when he possibly was born and where.  So far no info on when he arrived in Pennsylvania but assume in mid 1770's.  Have searched Scottish and Irish records when available but without a birth date has been impossible to know origins.  Any help will be greatly appreciated.