Security Writer 
Valve: “We need a credit card on file to prove you’re 18”
Me: “My account is 23 years old”
Valve: “That just proves your account is old”
Me: “A credit card just proves you know someone with a credit card”
George BI think Newgrounds has a "if your account is more than 10 years old then you are clearly over 18" somewhere in their age verification or at least they did when they first started doing it.