If enlisting, your nephew will have to go to boot camp (3 months) and then schooling first before an assignment is given. Depending on the outcome of the schooling and type of schooling, the assignment or orders are then given. I am rather suprised to hear they have been told that guam is it.
When my hubby enlisted about 15 yrs ago, we did not know his first assignment for the 1st year.
What rate (type of job) did your nephew get assigned?