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Try that link, see if that helps any. If not, tell us step by step what you are doing.

http://www.xbox.com/en-US/support/live/acc-passportlink.htm
That seems to hold the clue. But there are still problems. Let me run down the problem.
1. I linked my gametag. I entered in I was 16.
2. I tried linking another but it remembers the first and says I’m underage even though it say I’m 18.
3. I try to link the old to a new and it says I’m under 18.
4. I have tried multiple .net accounts.
5. I have tried creating a new one at xbox.com.
6. When I tried either email on the 360 it says neither are connected.

Hmmm… Seems like your best bet is giving the Xbox support line a call. I believe the number is 800-4MY-Xbox.

Oscar Cantu thank you. I didn’t get anywhere on any other site. Anyway I called tech support. Yesterday they hung up on me then I called and was tired of waiting so I hung up on them. After a half-hour of waiting today I found out all I needed to do was press y when it askjed for the email and recover it using xbox 180 live info.

Glad you got it working now. I hate it when it’s a tiny step I missed or something so mundane. See ya on Live!