The only John Dobbie in 1851 Names Index for Glasgow is aged 12.
I checked the 1861 Index and found this.
Census taken Glasgow, Clyde (644/5) Enum. dist. 43 page 11
John Dobbie age 25 born Edinburgh
Jane age 23 born Glasgow
John age 5 born Glasgow
Helen age 2 born Glasgow
IGI has the marriage for John and Jane.
18 aug 1854 Barony John Dobbie and Jane McIndoe
Also has the following children
Helen Dobbie 27 june 1855 Anderson, Glasgow (This child must have died as another Helen was born)
John Dobbie 27 aug 1856, Calton, Glasgow
Helen Greenhill Dobbie 5 aug 1859, Calton
Margaret McBeth Dobbie 17 jan 1862, Glasgow
Robert McIndoe Dobbie 15 feb 1864, Glasgow
William McBeth Dobbie 17 feb 1866, Glasgow
1855 births was a good year for information on certs.
As well as giving info. on where and when the parents married, they also gave father's age and place of birth..