If there is a hand written number on the board you can contact gordon and smith and see if they have a record of the board. Most shapers keep at least some info about every board they have made, identified by the number, and could probably tell you the age etc at least.
http://gordonandsmith.com/site/ If you are hoping for something worth a lot, there are about 5 old surfboards worth something (because of who owned them) and the rest are not worth anything. Old surfboards are not antiques, they are just old. (you can still use them for surfing, of course)