Where is the Wiki taking that date from, though? I don't recall seeing it anywhere. The timeline does seem a bit off, though. i feel like Giles is a bit younger than they claim.
Here it is! http://buffy.wikia.com/wiki/Rupert_Giles
On the biography section it says 1954, although, they don't have a specific reference for the date, I assumed they got it out of some Buffy comic. But yea, even if the year isn't exact, in the show they tried to make 16 year old Giles be Ripper, which is probably the mistake they made. I think besides that reference in Band Candy, Giles' "Ripper days" have been consistently placed in his early 20's.