William Joseph Humphreys

My search for William Humphreys has led me all over the place, and still I can find nothing on him except the births of his children and his death certificate which states that he was the son of William Humphreys, a wheelright, with mother unknown.He died 28th August 1933 in Byron Bay, New South Wales, Australia.He is buried in the Church of England cemetery, in Casino, NSW.He was born in Buckinghamshire, England and had been residing in the Australian Colonies for 85 years in NSW.. which would give us his birth around 1835, with the emigration date being 1849.
I found a William Humphreys at the age of 24 emigrated as an assisted British Immigrant in July 1849 on the ship Hope, book No 4A, page 138. This confirms the information on his death certificate, that when he died in 1933, had been in the Australian Colonies for 85 years, so he had emigrated in 1848/1849.
He was aged 24 in 1849 and so was born 1825. This date is not covered by the Civil Birth Registrations in England.The only William in Buckinghamshire, in the Parish of Chipping, Wycombe is found living in Prospect Cottage in the 1841 Census Index, being aged 10. This is the only one found that corresponds with the claim that he came from Wycombe. He is the son of William a butcher and Sophia with 5 siblings. In 1851 census of the same family, there is no mention of my William who by this time should have been 20.Therefore if this is my William, he would have been born about 1831.
According to the Birth Certificates that I have:
Eliza, being their second child, born 25 Mar 1878, William was 29, a labourer, born in Buckingham, England, married 1869 in Richmond Victoria to Emily formerly Crosby, 26 from Coventry, and informant being William Humphreys, father, birth registered 28 April, 1878.
Robert, the middle child, born 25 April 1880, William was 33, farmer from High Wycombe, England, married January 1870 Melbourne, Victoria to Emily Crosby, 28 from Coventry, England, birth registered 27 May 1880.
William Charles, the youngest, born 2 June, 1883, William was a 37 year old, a wheelwright from England being married to Emily Paxton Crosby, 30 from Englandon 28th September 1870, with the informant being Emily P Humphreys, from England, birth registered 30 June 1883.
I have not got Matilda's birth Certificate, but she is listed as born to William Humphrey and Emily in Inverell in 1881, registration no. 19272.
I have been unable to find the birth of Mary Ellen, born in 1877, but I have her marriage & death certificates, with parents' names.

The dates just don't make sense to me.According to Eliza, the first born, William would have been born about 1849,yet according to his death certificate, the date would be 1840.He could not have arrived in Australia in 1949 as a 24 year old.

Can someone help me out here.
Jane