Missouri allows a person at least 19 years of age — or 18 if a current or honorably discharged U.S. Armed Forces member — to carry a concealable firearm without a permit, provided the firearm is lawfully possessed and the person is not in a § 571.107 restricted area. The framework dates to SB 656 (2016), effective January 1, 2017.
"Subdivision (1) of subsection 1 of this section does not apply to any person nineteen years of age or older or eighteen years of age or older and a member of the United States Armed Forces, or honorably discharged from the United States Armed Forces, transporting a concealable firearm in the passenger compartment of a motor vehicle, so long as such concealable firearm is otherwise lawfully possessed."
RSMo § 571.030.3 (vehicle/age exception) and § 571.030.4 (permit exception) statute