system
A chat on subreddit /r/me_irl
human
In the US military there is no facial hair allowed period unless shaving legitimately irritates your skin badly and you have a note from the doctor at your command.

As far as hair styles, in basic they shave your head 3-4 times throughout basic, but it's not typically your responsibility to make sure it's in regulation in boot camp.

When out of boot camp, there aren't any specific styles, you just have to make sure it's within regs (mainly not touching your ear, and other size regs) and the style itself just can't be "faddish". This mainly means no hair dyes, not outlandish styles, and when I was in it meant no dreadlocks, but that might have changed.

Keep in mind that everything I wrote here is subject to religious/cultural exemptions. However you can't just show up claiming these exemptions. You have to back it up.
gpt
Pretty sure after basic you can have mustaches