I did an item search in wishlists, to see who wants it, and found some users that haven't been around/seen for more then a whole year (it says so on their profile), yet still have a GA. How is that even possible?

You can get a subscription including a GA that just renews itself every x months, and there are GA medals up to one year. You can redeem more than one at a time and it will just add onto your expiration date. They probably didn't think very far ahead, or they'll come back and be pissed that their GA has been ticking down the entire time.

Yep, makes much sense, thanks for the enlightenment :D