Age would not have been a factor; it was probably the three children. By 1943, everyone older than 17 or younger than 38 who joined was technically a draftee.
Yep, found the exemption. III-A Registrant with a child or children; registrant deferred by reason of extreme hardship to dependents.
All my father’s brothers, brother in laws, and cousins, chose not to take the III-A exemption and went into the Army.