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”
Ok this is interesting.
The desktop app has no such restrictions, only mobile.
yetzt@SecurityWriter using a desktop is dating yourself. as an old fart.
sortius 
@yetzt @SecurityWriter which is funny, because both my kids use computers mostly, not phones.
This explains why my 11 yo daughter has had no problems circumventing the under-16s ban
@sortius maybe being an old fart is more of a vibe, or maybe it's a retro trend like flared pants, that's getting cool again with whatever letter generation eleven year olds are.