Just noticed Mary was born in Borrowby not Robert, but that might make more sense.
1851 census:
HO107/2371, Folio 307, Page 15
Yorkshire Thirsk,
Long Street
Robert Long, h. mar, 66, Ag Lab, b. Yorks, Thirsk
Mary, wife, 64, Yorks, Borrowby
Hannah, dau, unm, 20, Servant, b. Thirsk
Thomas, grandson, 14, Ag Lab, b. Thirsk
One thing that's bothering me, the fact there might have been two grandchildren by the name of Thomas ?
* This might have to be treated with caution.
Added: Sorted, per the post below.
Pels.