Hi, I had the exact same problem and it took me ages to figure out what to do. It looks like my xbox live account was not linked to my ea origin account and so it couldn't verify my age and said I was too young!
Here's how I fixed it (without any 'help' from EA or MS):
1. Open up Origin on your PC and log in.
2. Go to the friends list and click on [+Add a friend]
- A window pops up with 'Import friends' on the left hand side and options to connect with facebook, xbox live, playstation network and ea account.
3. Click on the [Connect] button next to the Xbox Live logo.
- It takes you to the Windows live login screen.
4. Login with your Windows live email address and password.
- Magic. Your xbox live account is now linked to your ea origin account.
5. Verify by going to [Origin]->[Account Settings]->[About] and scroll down to the [Connected Accounts] section.
Why there isn't a button to link up or edit accounts in the main setting screen I don't know!