Age heaping is widely employed as an indicator of human capital, more specifically of numeracy. We re-examine the age heaping–numeracy link in the light of evidence from nineteenth-century Italian censuses, in which education explains little of the variation in age heaping. We argue that in general age heaping is most plausibly interpreted as an indicator of cultural, economic, and institutional modernization rather than a straightforward measure of individual cognitive skills. We do not rule out the use of age heaping as a numeracy indicator, but this needs to be done with research designs that are alert to historical specificities of the context under investigation.