I dont think there can be much doubt that the Robert in 1851 census reply 1 from Kay99 is the right one. He's a Pitman, 32, living in Byker, born Wallsend, with widowed mother Isabella. You also have the baptism for Robert, son of William, Pitman, and Isabella in Wallsend in 1819.
You have said that the 1852 marriage details say Robert is a Pitman, of Byker, age 28, father William is a Pitman, deceased.
All matches bar the age, but you have to bear in mind that Robert was marrying a much younger woman and may have been understating his age.
In the later census he consistently states he's born Wallsend and gives his age as :
1861 – age 39, so born around 1822.
1871 – age 48, so born around 1823.
1881 – age 65, so born around 1816.
So I think 1819 baptism is fine.
Alan.