The other aspect is, that pure serial numbers cannot affect the price - in theory if I know a lens is 10-15 years old I could attempt to negotiate a lower price from a private seller compared to a lens that's 1 year old (assuming else the same condition when looking at it).
A serial number would not allow you to distinguish those lenses.
A little reality check here: You MAY be able to negotiate based on lens age with an individual, amateur, or other non-serious or "motivated" seller, but if I am serious about recovering legitimate value from a piece of equipment I want to update or replace, you not very likely to advance the negotiation based only on the lens' chronological age.
It's meaningless anyway. The serial may indicate the lens was manufactured 12 years ago. But did it sit on a store shelf for three years or did it sell the week after it was made? Was it used daily by a working professional for 12 years, or was is taken out of the closet by a neurologist only to shoot Christmases and Muffy's wedding for 9 years?
If a lens is clean, well-maintained, and in good working order, you aren't going to get a discount from me just by pointing at the serial number.
To paraphrase the '92 Clinton campaign, "It's the condition, Stupid."