Whereas the wiki's definition for younger_male, older_male, younger_female, and older_female seems to imply that the tags fit even if the respective characters are within the same age group, the wiki definition for age_difference explicitly states that the tag is only for when the respective characters are within a different age group. This would make the implication of age_difference inaccurate as per the wiki for posts where despite characters having an age difference between them, they are within the same age group.