I would pass!
As in.. run 100mph the other direction. It infuriates me when people can be so horrid to someone trying to enjoy riding and lying like that!
If you are new to riding, do you have a trainer you can take with you? My advice would also be take plenty of pictures, and video and plonk it on here. Everyone has lots of advice and will guide you as best they can.
My second piece of advice would be to get the horse PPEd by a different vet to the one the seller will normally use; a vet will be able to tell you how old the horse is.