Enlistment-Ending Minor Malaise

Awesome McCoolname is strong, athletic, good at fighting, calm under pressure, and an unflinching patriot, and there may even be a draft going on. Why then, is he not in the military? The answer is surprisingly simple: They rejected (or discharged) him due to a minor health problem. While it may kill his military prospects, this health problem isn't nearly bad enough he can't get up to action hero adventures, but does explain why he's not doing his patriotic duty without being a draft dodger.

Examples of Enlistment-Ending Minor Malaise include:

Literature

• Owen Pitt of Monster Hunter International was raised to be a perfect soldier by his decorated veteran father who knew from his own encounters with the supernatural that one of his sons was doomed to central to the battle against the great old ones. When it came time to enlist, Owen was rejected for childhood asthma (which he no longer has) and flatfoot. Effectively free of his father's harsh training, Owen decides to become an accountant to get as far as possible from soldiery, until an encounter with his serial killer werewolf boss thrusts him into the world of professional monster hunting. Aside from being a poor runner, which is as much attributable to his massive size and heavy gear as it is his flatfoot, these cause Owen little trouble.
• John Abbott of Abbott in Darkness is unable to continue the family tradition of being military pilots due to being diagnosed with Marfan Syndrome, rendering him unable to endure pulling Gs.

Live-Action TV

• While most of the Dad's Army cast are relegated to the Home Guard for clear cases of being too old for military service, its younger members are in the Home Guard instead of the army due to examples of this. Joe Walker is allergic to ration staple corned beef (though the loss in a BBC archive purge of its debut episode The Loneliness of the Long Distance Walker and his Black Marketeer stats give many the impression it's fake) while Frank Pike has a rare blood type.