I agree that 7 is a young "curator" but so is 12 (if born in 1820). I think as Justin says he worked his way up to curator - perhaps beginning in 1832 as "broom boy" - Remember that there were no child labour laws back then. See 1861 census attached giving age 36 and birthplace Scotland. This is...
Well, with the site down had a chance to do a bit more on Louis.
Firstly the 1851 Census tells me two things firstly he was Scottish and second he may have been younger than we thought (ie born c. 1825).
So I found a baptism record for a Louis Fraser
29 December 1825
Louis Fraser is a tricky chap!
I can tell you that his life was not a constant one - although he was born to a Gent (Hugh) and his marriage was a good one by the time his daughter Mary Alice was born in 1847 they were in the workhouse.
In 1861 they were living in Manchester.
In 1865 Louis was...