PPL probably not the best idea for a potential service pilot. Military flying is very different and the not inconsiderable expense might be better spent.
ATC can provide much for him - including flying at little or no cost to you. And instructing ab initios can be easier when you have a blank sheet of paper, rather than having to "unlearn" civilian practices and procedures.
Away from flying, ATC can do lots for personal development as I suppose we call it now - Air Cadets are the biggest particpant in the Duke of E's Awards in UK for example, and Gold D of E is one of the best things to have on any CV!