I OC'd while under 21. Also had my CCW while under 21.
My brother is currently OC'ing and he is under 21.
In ID you can OC a rifle at 12 and pistol at 14. The pistol in particular can only be done on the way to a range/shooting activity without parental presence. At 16 you can OC a pistol anywhere - within state law - as long as you have a written letter of permission from your parent or legal guardian.
18 and up is no regs on OC!
I'd suggest you obtain a pocket recorder to keep in your pocket if you look young though.
Also read the threads on here from Saint, Idaho Corsair, and myself. I have one posting that lists most of the laws regarding OC here in ID.
Welcome to OCDO!