Hi Kathy,
Death cert info is only as good as the persons knowledge who supplied the info. They are generally classed as the "LEAST" reliable of all certs.
Pre 1896 NSW Marriage Certs are touch and go as it was up to the Church to collect parental information, age, birthplace etc. If you have his marriage cert you need to contact the Church named on the cert and enquire where you can access their archived records.
Some Churches have their own copies and other times copies are held by Family History Societies or major libraries.
A birth certificate for one of his children should state his age and where he was born. This information is usually supplied by the parents at the time of the event, so is generally more reliable than a death cert.
Your best chance though is to access the Church records.
Kellie