I have to hope this guy wasn't an NCO but....

In my MOS when I was in the most common age that people made E5 was 21 because our promotion points were so low (350) that basically anyone that went to the board got promoted and you could go to the board at 3 years time in service.

We had a high speed guy get promoted while we were deployed that couldn't drink with us when we got back because he was 20.