Hmm. You might have a problem . . . although, if you made the big money when you were 18+, you might be fine. FT's rather understanding . . . they're not out to take all your money if you made any sort of mistake. I know this isn't the same situation at all, but I had an FT account a while back and then stopped playing and requested that they close it. When I decided to play again, I opened up a new account and made quite a bit of money ($300+ profits) and when I went to cash out, they found out that I had a previous account and closed my recent account because it was against the rules to have two (I didn't know my old account was still in existence...but aparently when they 'close' an account, it's still there, but frozen, and can be reopened upon request). I freaked out and thought that all the profits on my recently closed account would be lost, but they promptly let me know that they would transfer the remaining balance of the closed account into the old one and reopen the old one and all was well.
In short, I think they're very understanding and helpful. Good luck!