Hi Galvin,
I see from your tree that you think he was from Co Kerry in Ireland, try this link, there are a few marriages and babtisms on there that may help.
http://irishgenealogy.ie/
mum mum
A copy of the 1860 birth cert for Charles is also there - putative father John Galvin, General Dealer, 37, born London, England, mother Mary Morrison, formerly McNichol, 27, born Glasgow, Scotland. Parents not married.
Details on the death index appear to contradict John's place of birth, but I would believe the birth cert before anything else. Perhaps his family was from Kerry, but he was born in London.
The "Severn" arrival in 1852 simply says John Galvin, aged 25, Clerk, English (out of a choice of English, Scottish or Irish) The age given on the online indexes is incorrect.
On a tangent - there is a marriage for a Mary McNichol (aged 20) and John Morrison (aged 28) (extracted) at Paisley in Renfrewshire on 14 May 1852, and an immigration record for a couple by this name and with the same ages arriving at Melbourne on the "Wanata" in Oct 1852. Perhaps John Galvin and Mary did not marry because one of them was not free to do so.
Debra