Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
cŏ-aetānĕus, i, m. [aetas], one of the same age; a contemporary (post-class.), App M. 8, p. 204, 5; Tert. adv. Herm. 6; Vulg. Gal. 1, 14.