Increase the minimum age for military service from 18 to 21, or limit under-21s to noncombat roles away from foreigners.

Military service means representing the United States and making life or death decisions, both acts that benefit from maturity. Increase the minimum age for military recruitment from 18 to 21, to increase the quality of decision-making by US troops. Or, mandate younger soldiers to roles where poor decisions will have less of an impact on the perception of the United States or on the lives of non-US nationals.