Literal Translation
It’s been chandeliers!
Actual Meaning
It’s been ages!
Etymology
While ‘lustre’ = chandelier, that’s not actually what this expression means. The word, borrowed from the Latin ‘lustrum’ – probably derived from “luere” meaning ‘to wash, to bathe’ – has been found in French since the 13th century. In Roman antiquity, it was the name given to a ceremony celebrated in the form of a sacrificial offering every five years by the censors at the end of the census, to purify the Roman people. It took place when the censors had finished drawing up the official list of Roman citizens. The word then came to refer, by metonymy, to a period of five years.
Thus, when we say ‘ça fait des lustres’, it literally means ‘several periods of five years’, i.e. the equivalent of several five-year terms. By extension, the expression refers to a very long period of time.