The IGI gives this information extracted from the parish register
JOHN BOYARD
Christening: 24 JAN 1814 Mancetter, Warwick
Father: JOHN BOYARD
Mother: ANNE
WILLIAM BOYARD
Christening: 25 JUL 1819 Mancetter, Warwick
Father: JOHN BOYARD
Mother: ANN
ROBERT BOYARD
Christening: 22 FEB 1814 Mancetter, Warwick
Father: ROBERT BOYARD
Mother: CATHERINE
SARAH BOYARD
Christening: 21 OCT 1816 Mancetter, Warwick
Father: ROBERT BOYARD
Mother: CATHERINE
MARY BOYARD
Christening: 18 MAY 1819 Mancetter, Warwick
Father: ROBERT BOYARD
Mother: CATHERINE
CAROLINE BIARD
Christening: 18 AUG 1822 Mancetter, Warwick
Father: ROBERT BIARD
Mother: CATHERINE and from the civil registration
Deaths Dec 1900
Boyard Robert 82 Walsall 6b 459
which gives Robert a birth date of circa 1818
1891 census ?
1881 census aged 62 = birth year circa 1819
1871 census aged 51 = birth year circa 1820
1861 census aged 43 = birth year circa 1818
1851 census aged 33 = birth year circa 1818
1841 census aged 20 = birth year between 1817 and 1821
So he is pretty consistent with his age and never really goes before 1818. He looks to be the child 'sandwiched' between John and William.
Deaths Sep 1866
BOYARD William 46 Walsall 6b 323
I don't think Walsall parish registers are on the IGI and that may be where you have to look for Robert and Mary's baptisms (even if Robert was born in Warwickshire he could have been baptised later as his younger sister Sarah was) and for the burials of the two Johns - father and son (Mancetter is on the National Burial index - their burials are not there. The John Boyard death registered Atherstone in 1837 is a child of 2).
The Birmingham and Midland Society for Genealogy and Heraldry have a county wide (I think) burial index for Staffordshire up to 1837 and also a probate index.
http://www.bmsgh.org/It might also be worth looking at their marriage index for Warwickshire for the marriage of John and Ann.
Regards
Valda