What the hell is a 20 year old minor? I was in the Marines when I was 17.
Minor in possession
What is minor in possession?
When a person age 13–17 signs a diversion agreement or is convicted of possession of alcohol. (Age is determined by the incident date.)
When a person age 13–20 signs a diversion agreement or is convicted of a drug offense. (Age is determined by incident date.)
When a person under age 18 pleads guilty or is found guilty of illegal possession of a firearm while in a vehicle.
When a person under age 18 commits any offense while armed with a firearm in which a motor vehicle served an integral function.
When a person age 13–17 is convicted of any offense involving a firearm, whether or not it is related to using a motor vehicle.
http://www.dol.wa.gov/driverslicense/minor.html
If you have problems with the term minor, you need to take it up with the legislature.