Sterilization is a procedure used to prevent couples from having children. Different procedures are performed depending on the sex of the patient.
For women, tubal ligation is the surgical procedure performed, commonly known as "tying the tubes". A woman's fallopian tubes transport mature eggs from the ovary to the uterus approximately once a month. When sperm travels from the uterus through the fallopian tubes toward the ovary, it may encounter a mature egg -- and fertilization may result. Tubal ligation permanently sterilizes a woman by preventing transport of the egg (ovum) to the uterus, and by blocking the passage of sperm up the tube to the ovulating ovary where fertilization normally occurs.
For men, a vasectomy is a surgery performed to "tie the tubes" (vas deferens) of a man, which causes permanent sterility by preventing transport of sperm out of the testes.
Certain federal programs have minimum age requirements, typically 21 years old. States have held that a person must be of legal age, which varies by state (usually between 18-21), in order to give informed consent to the procedure.