Make sure to bring an ID and you should be fine, as long as you book a standard adult ticket. ID is rarely checked, especially on minors. If you have an ID without your date of birth and act responsible while onboard there is nothing they can really do. I travelled on the Crescent, Carolinian, Silver Star, and Autumn Express alone all before the age of 16. In addition, the train experience is far superior as an adult. When I travelled as a minor, they just had me sit in the cafe car and I wasn't even free to walk around the train.
Please do not supply a suggestion such as this. Have you any idea what sort of thing could happen to an unaccompanied minor we don't know about?
And once you're on the train (breaking the minor policy) there's nothing you can do? Is that why I've had two of my trains met by Amtrak police to have minors without paperwork taken off? One just last week, in fact. And excuse my language, but the parents were real **** bags trying to take full advantage of Amtrak. ..They bought the 15 year old a senior fare.
But anyway, it was how old they looked that caught the crew's eye, not the fare paid. Please do not try to be "smart" and work your way around the system, or else you may find yourself in a REAL bad situation.