Seller says 16.5 inch from c/c if that's centre of b/b to centre of top tube then I would say it's a 18inch frame as gt used to measure from b/b to top of seat tube(where the seatpost goes in)
Thought it was other way for some reason,never mind.
I guess he could always look at the stamps near the serial number easier than measuring?
Did the do a 16.5 as he says in above eBay ad?