Okay, a bunch of problems with that.
First, if you make everyone serve two years, how are you going to pay them? if you have 5 million 18 year olds every year, to be paid an E-1 salary - 24000 a year. That would be 120 BILLION a year. And that's not counting the costs of housing, feeding, equipping and training them.
Second- Who is going to train them, exactly? You would need a lot of drill instructors, more than we have even if we activate all the reserves.
Third, what are you going to have them all do, exactly? Sure, you could fill out all the active and reserve component units with draftees, but what would you do with the excess people.
Fourth, what do you do about the people who are physically or mentally unfit for service?