What does "Four-F." mean? [closed]

Solution 1:

It's a classification for military service. 4-F means "Registrant not acceptable for military service." See https://en.wikipedia.org/wiki/Selective_Service_System#Classifications

The context clue here you might have used to deduce an area of inquiry would be the reference to a "draft board", which is part of the Selective Service System that determines the eligibility and thus the classification of potential draftees.