By investigating the relationship between CEO age and firm innovation, this paper explores whether younger CEOs drive innovation and what propels them to innovate. In terms of which CEOs have incentives to actively participate in innovation, the personal characteristics of CEOs are not adequately addressed. Therefore, this paper contributes to providing further evidence of the literature on corporate innovation, by checking which of two hypotheses, market learning hypothesis or managerial signaling hypothesis, about younger CEO’s career concerns is suitable for Korean listed firms. The empirical results are as follows. For manufacturing firms listed on two Korean stock markets from 2000 to 2016, this paper finds that CEO age has a negative effect on firm innovation measured by the number of patent applications. Generating three cohorts of CEOs by age: under 50, between 50 and 59, and 60 and above, this paper also shows that younger CEOs under 50 are more likely to take part in firm innovation than older CEOs over 60. These findings remain robust in estimating Tobit, Poisson, and negative binomial models considering the fact that the number of patent applications has the non-negative nature and the non-trivial portions of sample firms with zeros, in using samples reconstructed from the methods of propensity score matching, and in conducting firm- and CEO-fixed effect models controlling for unobservable firms’ or CEOs’ characteristics. These findings indicate that managerial signaling hypothesis is supported for younger CEOs in Korean firms. A possible explanation is that younger CEOs with career concerns have more incentives to gain reputations as great inventors or innovators and then to enjoy the benefits from these reputations in their longer career horizons, by signaling CEOs’ abilities through successful innovation, such as patents, than older CEOs do. In addition, this paper also finds that shorter-tenured younger CEOs (that is, younger CEOs with longer career horizons) more actively engage in firm innovation than longertenured younger CEOs (that is, younger CEOs with shorter career horizons). This additional test also indicates that younger CEOs in Korean firms want to delight in the benefits from reputations acquired from labor markets as innovators during their career horizons. This paper reconfirms that the predictions in managerial signaling hypothesis are consistent with younger CEOs in Korean firms, by providing evidence that they do not participate in firm innovation due to their overconfidence. Finally, this paper divides the sample firms into high- and lowtechnology firms based on technological levels of industries to which the firms belong, and into Chaebol and non-Chaebol firms following up the classification of the Korea Fair Trade Commissions. For all subsamples, the findings in this paper also appear, while there are statistical differences in the effects of CEO age on firm innovation. From the findings, younger CEOs also have incentives to participate in firm innovation that requires long-term efforts, is more likely to fail, and has uncertain results. This paper provides implications that providing incentives to help younger CEOs manage their careers, such as reputation or ability is important to drive firm innovation.