@Erikus Unfortunately, you're stuck, When your account is setup as an underage account; it's set that way forever, regardless of your age. In fact, if you set up an underage account on a device (at least an iOS device using the Game Center), then even if you start over with a new over-age account, it'll be treated as an underage account.
My daughter started an account on my iPhone years ago, and got me hooked. I started a new account for me on the iPad. I can play my account on either device, by signing into the Gamecenter. When I play on the iPad, everything is fine, but when I play on the phone, my account is treated as underage account, and I can't read the in-game chat messages, or TW guild orders, etc.