RichardMannion,
I got the Plat when I was 20 or 21. That wasn't very long ago. Mine is a US card. And when I was 20, I looked about 17.

Not only am I a young guy, but I'm a cheapskate -- so when I first got the Plat, I'd get a big kick out of using it at Motel 6 or Denny's.
I know of some Centurion cardholders around 18, but it's all off their parents' accounts. I must admit I do have some card envy, but my spending isn't nearly high enough to get me the Centurion. Ahh well; card colors aren't what's really important in life anyway.