In 1901 John was 17 - and as you say was a Dock Labourer -and living at 31 Keightley Street, Birkenhead - which still exists.Charles, his father, was aged 54 and his wife Mary E, Beattie was 46.Mary was born in Liverpool. They had with them eight children all born in Birkenhead. Ages were William (21); Robert (19); John (17); Edward (14); Helena (12); Edith (11); David (9) and George (7).Also with them was Mary McVey (70) born in Liverpool and given as Aunt - to Charles.
I hope this helps.
Do you have access to earlier census returns and birth, marriage and death certificates?