Those Army commercials that show young people talking with their parents about going into the military walk a very fine line in my view. In my opinion, no one thinking about going into the military should involve their parents or siblings in the decision process. (It would be ok to say, "I've made this decision, now ...".) It isn't a matter of independence, it is laying that "responsible for him/her going in" trip on them in case something happens.
Unless they are 17 years old, in which case they need parental consent.
It all depends on whether the parents / siblings are giving advice or making the decision. The former is a good idea; the latter is a bad idea.