I understand that the majority of the military IS that age range and are from various backgrounds. What can be frustrating is that when the general population is non-military and has little to no exposure to persons in the military, they see the media portray military personnel as the kid that joined to get out of trouble, or the kid from a broken home. I agree that is very impressive that these people have chosen to join and get themselves on the straight and narrow. However, for someone who is a middle America, college educated person who chooses and works hard to get into the military through OCS, Academy or rotc instead of pursuing a career in something more commercial or "ordinary" (business, etc.) it can be frustrating for people to say "why would you want to do that?" because all they see in the military is the kid from your HS class with failing grades and nowhere else to go.
All that being said, the series has been showing personnel from all walks of life as its progressed so that gripe is gone.
Gripe all you want, it's reality. Go to sea and see for yourself.