I don't know if this is correct Andrew but may explain his absence in 1911 census.
1901 census:
Hinnard,Ouley,co Down
Andrew Graham 32 Presbyterian born co Down farmer single (living with his mother Elizabeth age 60 widow and his brother Samuel age 35)
1911 will calendars (Proni)
Elizabeth Graham died 19 April 1911 granted admin at Belfast to Andrew Graham farmer