I don't think there is a way to 'age' a weber carb. BUT maybe you could go by what type you have and refer that back to what vehicle that particular Weber is fitted to as OE, then you could get a period of time?
Having said that, I have just spent almost an hour trying to pin point some webers to car makes to give an example and not even that would work I am now thinking.
I am pretty sure the different numbers just give you an idea of what the factory settings are of that particular Weber. But since they get changed over the years from being on different engines they develop an identity of their own anyway.
What letters/numbers do you have on your carbs that you want to identify?