The answers so far have only considered the "front line" aspect of an army, but there are vast swathes of military service that never require you to raise a weapon in anger.

Command, logistics, quartermaster, intelligence, recruitment, training, catering, maintenance, medical, communications, as examples that exist throughout the ages. Most of these things requiring far more in the way of soft skills than the simple strength that's being focused on and all of them essential to the functioning of a large military. In earlier militaries you'll get grooms and animal handlers, squires to help the knights. Pick your era and you'll probably find young boys performing these roles, because they don't have the strength to fight themselves.

A fully formed army can find a role for anyone, regardless of strength, ability or even disability.

The answers so far have only considered the "front line" aspect of an army, but there are vast swathes of military service that never require you to raise a weapon in anger and also leave you at far lower risk of being on the wrong end of one.

Command, logistics, quartermaster, intelligence, recruitment, training, catering, maintenance, medical, communications, as examples that exist throughout the ages. Most of these things requiring far more in the way of soft skills than the simple strength that's being focused on and all of them essential to the functioning of a large military. In earlier militaries you'll get grooms and animal handlers, squires to help the knights. Pick your era and you'll probably find young boys performing these roles, because they don't have the strength to fight themselves.

A fully formed army can find a role for anyone, regardless of strength, ability or even disability.