No. That decision is made at the ballot box.
IMHO, conscription is the sole justification for 18-year-old suffrage.
In fact, due to conscription, I advocate full rights, privileges and responsibilities of adulthood for 18-year-olds... voting, drinking, whatever...
Remove the potential for conscription, and I become a staunch advocate of traditional 21-year-old adulthood.
At 18, the teenagers' heads are too full of adolescent mush to be considered adults.
Democracy and liberty are often confused. Democracy simply means rule by vote. Liberty means that even in a democracy (or a democratic republic) there are some decisions that the majority cannot make. The decision to sacrifice one's life in a war is one of those decisions.
In other words, your life is your own, and not the property of 51% of the population.
At 30, many adults' heads are too full of adolescent mush to be considered adults. Yet they are.