No, that was wrong about James being younger - he was also older than they said in later censuses:

1881 census:

MCMULLEN, Jas Head Married M 30 1851 Dyer Manchester, Lancashire
MCMULLEN, Margaret Wife Married F 36 1845 Dyer Wife Manchester, Lancashire
MCMULLEN, Mary E Daughter Single F 10 1871 Scholar Manchester, Lancashire
MCMULLEN, Jas Son Single M 8 1873 Scholar Manchester, Lancashire
MCMULLEN, Elizabeth Daughter Single F 3 1878 Manchester, Lancashire
MCMULLEN, Albert Son Single M 0 1881 Manchester, Lancashire
BENT, Mary Ann Boarder Widow F 67 1814 Fustain Cutter Manchester, Lancashire
Piece: 3989
Folio: 51
Page: 6
Registration District: Manchester
Civil Parish: Manchester
Address: 36, Tickle St, Manchester
County: Lancashire

Sue