Under Scotland, Select births and Baptisms 1564-1950 I found the following records on Ancestry.com:
James Robertson male born: 16 Feb 1778 Baptism, 22 Feb 1778 in Perth, Perth, Scotland, Father: Daniel Robertson Mother Ann Couts. Film #1040330
James Robertson male born: 8 April 1780. Baptism 13 Apr 1780 in Perth, Perth, Scotland. Father: James Robertson Mother: Ann Wedderspoon. film # 1040330
James Robertson, male, born: 17 Jul 1780 Baptism 20 Jul 1780 in Perth, Perth, Scotland. household members were; James Robertson, Christian Robertson, and James Robertson. film # 1040330
Magdalene Walker, female, born 29 Mar 1783 Rhynd, Perth, Scotland Father: Henry Walker, Mother: Margarete Bruce film # 1040136
I also found the same marriage proof on Ancestry.com Scotland, Select Marriages 1561-1910. Maidline Walker, female, marriage 4 Jan 1807 place: Kinnoul, Perth, Scotland. Spouse; James Robertson film # 1040120
I could not find a birth date for James Robertson for 1779, just the ones I have given you for 1778, and for 1780.