Maybe you can pass a birth date in as a parameter? It doesn't seem to matter what it is as long as the calculated age is 18 or over I believe. Of course you probably know all of this so I will shut up now. In a minute. Nothing to do with your code but I never realized that Steam marks the Demo listing as owned for any full game I own whether I downloaded the demo or not.
The code is just doing a mass HTTP GET request for all of the links on the page that lead to steampowered.com/app/ or steampowered.com/sub/ which seems to randomly hit a wall. Unfortunately, it's not smart enough to know "if it asks for your age, enter 1/1/1900". I just tell it "go get this file, and look for the green banner". So if it gets something other than what it expects, it will just report back "nope, I didn't see the green banner so you must not own this".
Also, Steam uses the same link for the full version and the demo of games. So with this same logic, all of the demos in the search will show a green banner if you own the full game.