Your son would not be vulnerable until he is 20.
http://www.sss.gov/viet.htm
The bone I have to pick with SS is that we do not register women as we do men.
Thanks for the info but at the link you provided it states:
"Under the current draft law, a college student can have his induction postponed only until the end of the current semester. A senior can be postponed until the end of the academic year."
If he's 18 when he enters college next September and the draft is instituted shortly thereafter...he can be inducted at the end of his current semester.