Last year my friend's dad walked up to the window and asked for an adult and 3 children (under 12) passes. We were all 17 but the guy at the window couldn't see us.
Haha, yea, I've done it, it saved me $40 over 2 days.
I asked for one youth (under 18), and he asked if I had ID, nope, I'm only 17. So then he asked when is your birthday, and I just added one year onto my birth year.