One of my ancestors is a Jane Mearns confirmed as being born in Bourtie around 1801 ( from Fyvie 1851 census).
IGI agrees with this christening date, daughter of Robert Mearns and Isabel NIcol. According to LDS IGI she has a brother, James born in Bourtie in 1806. Could this be the same as your James ? If so he could not have married in 1816 , but 1839 would be possible.