31 CFR §363.11

Only an individual or an entity is eligible to open a TreasuryDirect account. In order to open a TreasuryDirect account, an individual or entity account manager must have a valid social security number (SSN), be 18 years of age or over, and be legally competent. An entity must have a valid SSN or employer identification number. The account owner must have a United States address of record and have an account at a United States depository financial institution that will accept debits and credits using the Automated Clearing House method of payment.