My son is a Sergeant in Special Forces, he has about 4 or 5 years to his 20. Does anyone know how likely this is to happen to him?
Nobody is completely safe until 18 years. However, I am very glad that he is in special forces because so far they have been completely safe.
The other consideration is whether he is an officer or enlisted. It is sometimes easier in the enlisted ranks to make sufficient rank early and not have to worry about being separated. In the officer ranks it depends on smaller groups of people and how many peers you have to compete with.
As long as your son is moving along with his peers he shouldn't have any issues. Once he makes it to year 18 he will be safe from this issue.
Not likely. SF and a SGT, chances are they will keep him around until they cannot squeeze any more out of him.
These are generally officers who have redundant skill sets.
But as a contractor, and a military retiree, I have seen it before.
But nothing like the purges back in the early 80's when the Marine Corps, bounced a bunch of late Vietnam Vets out.