I think discussion of rank has gotten us into the weeds. The issue is when does a person become an adult. I grew up on the front row of the conflict. I was 18 years & 3 months old when I arrived in Germany as a soldier. I was an adult. Meanwhile I made some friends who were older then me but children of soldiers (or staff supporting us) and they were kids.
True story - I was in a group that was told that we could never ask a daughter out. Though I was closer to her in age than her boyfriend at that moment. Long after it mattered the mother and I talked and she found out. She was mortified as she just thought of soldier = too old.
Even now I have a young man who is now on extension (thanks COVID) and he is not an adult. I think highly of him, but he is an old about to be high school senior and not an adult.