There is a widespread belief that older teachers have less innovativeness than younger ones; however, the evidence backing this is contradictory. This study examined the relation between age and teacher innovativeness—that is, the extent to which teachers at school are open for innovation and willing to take actions towards it— at the teacher and school level, including contextual effects. Using data from the OECD’s Teaching and Learning International Survey (TALIS) 2018 (a total of 154,959 teachers in 9,185 lower-secondary schools from 48 countries), the effects of age on teacher innovativeness at the teacher and school level was tested via multi-group multilevel structural equation modeling. A doubly manifest contextual model and a manifest-latent contextual model were applied to test consistency when controlled and not controlled for sampling error due to the sampling of individuals in the aggregation of characteristics from the teacher level (L1) to school level (L2). These models showed that the individual perception of teacher innovativeness of the teacher team (L1-TEAM) was positively associated with individual teacher age (L1-AGE) but negatively related to age school composition (L2-AGE). Nevertheless, no consistent evidence supported the effect of age school composition (L2-AGE) on the teacher innovativeness at the school (L2-TEAM) across countries—a ﬁnding with significant policy implications. The present study concludes with several implications at different levels, including educational policymaking, school practice, applied research, and directions for further educational innovation research.