I am not a lawyer and this is not legal advice. For legal advice consult an attorney.
I am a Federally Licensed Firearms Dealer, and a Wisconsin peace officer.
A person under 21 cannot purchase a handgun from a licensed dealer.
A person over 18 can have a handgun given to them, and can posses a handgun in Wisconsin.
A Person over 18 but under 21 can legally open carry but cannot get a concealed carry license.
So what could trip a 19 year old up is the school zone problem. Without a CCW license one cannot carry within 1000 feet of a school zone, openly or concealed. Be careful when in a city/town/village area.
And then there is the problem of cops that are ignorant of the law. Spending 72 hours in jail and then not getting charged still sucks even after you receive your settlement check.
I am not a lawyer, this has not been legal advice.