Agree

Yvonne what were
Charles John's ages on both his marriage certificates please? Could we also have the full dates of his marriages.Surely a family member knows the date of his birthday ie day and month.
Charles says he was born Rockhampton so in the absence of any registration you may have to accept that you will find nothing more. In a number of colonies [ie before Federation] births not registered within a prescribed period incurred fines.
Did you follow up the possibility of baptism record at Rockhampton?
You wrote that Charles
DAVIS and Martha
STEVENS married in Dec qtr 1881 and arrived Qld 14 Sep 1883. Charles Jnr could not have been born on board as he would have been 53 years of age in Oct 1936 when he died. Charles was born late [after Oct] 1883 or before Oct 1884 at Rockhampton with his brother's birth 21 Oct 1886 in Orange NSW.
It would appear that Martha was also known as Mary Maud.
Are you convinced that Charles Jnr was educated in England? I cannot see a UK outgoing passenger record for a Charles
DAVIS born c1884 to Western Australia arriving prior to his first marriage.
Cheers

Cando