Based on your answers, you cannot apply for an eTA. You may need a visa or other type of travel document to travel to Canada.
As a U.S. citizen, you are exempt from the eTA requirement. You do not need an eTA to travel to Canada. Make sure to travel with valid proof of U.S. citizenship such as a passport and other acceptable travel documents.
Passport details of applicant
You must be at least 18 years of age to apply or apply on behalf of someone. A parent/guardian or a representative must answer Yes to the question "Are you a representative or a parent/guardian applying on behalf of an eTA applicant?" and complete the additional questions.
You entered a date of birth that is less than 18 years of age. If you are under 18, you cannot use this form. An adult must apply for you. This person can be a representative or a parent/guardian. They must restart the form and answer 'yes' to the "are you applying on behalf of someone?", and 'yes' to the 'are you applying on behalf of a minor child?' questions.
You indicate that you want to apply on behalf of a minor. To continue, you need to enter a date of birth that is less than 18 years of age. If you want to apply for an adult, return to the first screen and change your answer for "Are you applying on behalf of a minor child?" to "No".
Personal details of applicant
Residential address - Enter your permanent home address. Do not enter an address where you live temporarily.