John Minahan : Short Biography

In Irish Catholic Parish register records, there is a Killaloe baptism record for John, child of parents Charles and Mary (O')Keefe, for August 1835 and one for brother Charles for 1848.  John and brother Charles migrated to Australia in 1871, when John's age was noted as 23 years, (thus birth year c. 1848) and Charles as 26 yrs.  I suspect their ages may have been swapped and John was the elder.  John eventually moved to Tasmania after living in Melbourne for some years and died in 1911 in Franklin, Tasmania, aged 67 (thus birth year c. 1844).  Different records indicate a roughly 10 year discrepancy in John's date of birth.  Was John born in 1835 or 1845?  To be further researched!