Potential Texas drivers who are under the age of ____ must have their instruction permit or driver's license applications signed by a parent, guardian, or, if neither are available, a responsible employer.

Potential Texas drivers who are under the age of eighteen must have their instruction permit or driver's license application signed by a parent, guardian, or, if neither are available, a responsible employer. [Minors; Chapter 1: Your License to Drive; Texas Driver's Handbook]