Determining the age and value of old NIB Lego sets I have several old Lego sets, new in box.  Maybe 20 years old or more.  How to determine the age and value of these old Lego sets?
I would suggest going to Bricklink and entering the set numbers in.  You will find the information on the sets you have and, if it isn't extremely rare, a price guide with information on how much the set has sold for in the past and how much it's currently selling for.  

Bricklink: https://www.bricklink.com/v2/main.page  

There is a lot of information on this site that you may find useful, here is a link to one of the more recent inquiries with an answer and more information.  

Advice on selling a lot of Lego?