Which clinical scenario best indicates initiating B12 supplementation in an older adult?

A 60-year-old with elevated serum B12 and polycythemia who exercises regularly; supplementation is indicated to further increase red cell production.

An 80-year-old with documented atrophic gastritis and low serum B12 levels despite adequate dietary intake, where reduced intrinsic factor and gastric acid likely impair absorption.

A 55-year-old with normal hemoglobin, normal neurologic exam, and vegan diet who eats plenty of fortified grains but refuses supplements for personal preference.

A 70-year-old with normal B12 levels and no gastrointestinal disease but who refuses sunlight exposure; supplementation is unnecessary because sunlight affects only vitamin D, not B12.