Which of the following is a reason a soldier may be ineligible for reenlistment?

A soldier may be ineligible for reenlistment for several specific reasons, and one of the most significant factors is being flagged or barred. Being flagged indicates that the soldier has a disciplinary or performance issue that necessitates their temporary removal from certain duties or opportunities, including reenlistment. Flags are typically used to highlight issues such as failure to maintain Army standards or pending adverse actions, which directly affect a soldier's eligibility to continue serving.

Lack of promotion, exceeding the maximum age, or merely completing training do not inherently disqualify a soldier from reenlistment. For example, soldiers may reenlist after they have completed their training or even if they have not been promoted within their current rank. Exceeding the maximum age could impact initial enlistment but doesn’t typically apply in the same way for reenlistment, as there are waivers available depending on the circumstances. Thus, being flagged or barred is the most critical and direct reason for ineligibility for reenlistment among the given choices.