The 1841 census has his age as 70 and Ann's as 60 both born in Dorset.
As ages were rounded down 70 would put his age as 70 - 74 ie born c1766 -1770.
In 1851 Ann is age 73. I presume this is her christening
Ann Lacy
birth 14 Mar 1779 OLD MEETING HILL STREET-PRESBYTERIAN,POOLE,DORSET
parents Thos. Lacy & Ann
Did they marry at the same church? The marriage could give some clues to the origin of John.
Rosie