My answer to How would a United States military draft work?
Answer by Ken Larson:
The Selective Service System has been in existence or many years and is the basis for establishing the pool of eligible draftees.
It remains a public law to register in the Selective Service System at age 18.
The draft has not been active for many years.
In the event the need for a draft arises, the government will direct the methodology for selecting draftees from the Selective Service Pool.