Hi Johnsam93,
Welcome to RChat,
If so, was he travelling with anyone else as he would only have been around 16 years old?
I am not at all surprised that he was not travelling with any immediate family, there's many passenger lists from that decade and from the 1850's with teenage boys and girls travelling half way around the globe to come to either Australia or New Zealand. In my own tree I have noticed a 15 year old boy, and an 11 year old boy, both in the 1850's, a 16 year old girl in the late 1840's, an 18 year old in the 1860's. The 16 year old girl could read and write, but the others had not yet learned those skills.
He would have paid adult fare at age 16, and perhaps the motivating factor was the gold rush that had commenced in the early 1850's.
I note that a Miss Bennett (no initials) age 17, returned to Britain on the SS Great Britain in March 1868 ... if this is the Elizabeth Bennett who arrived in Feb 1868m then she celebrated her birthday in Victoria before returning... perhaps she was a member of the crew

Outward and Inward for Victoria (are indexes, and may not include all arrivals/departures)
http://guides.slv.vic.gov.au/content.php?pid=99868&sid=753618Cheers, JM