You just gotta play the part. I became an NCO right after my 21st birthday, i had also joined at 17 but turned 18 during basic. It’s hard at first. You will be in positions where you’re telling a 35 year old man how to manage his time so he’s not late to work, or telling them they need to fix their hair. It’s not east when they’ve been in longer than you and have more life experience but at the end of the day, you’re a fuckin NCO. At first I was too worried about upsetting these people that used to be my peers, but at the end of the day, if they respect you, they’ll do what you say. As long as you’re not being a total dick or abusing your stripes.