In the environment in which an increasing number of older travelers are participating in online tourism platforms, for older travelers who face multiple barriers in using e-commerce, it is essential to identify factors promoting older travelers' website usage for their well-being and sustainable travel industry. This study aims to identify the key factors of website atmosphere for enhancing older travelers' familiarity, investigate the relationship between older adults' website familiarity and revisit intention, and test the moderating role of cognitive age. A web-based survey was conducted, and the sample consisted of 305 US residents 50 years of age and older who had experienced travel websites. The results indicated that three subdimensions of older travelers' website familiarity-informativeness, effectiveness, and entertainment-positively influence their website familiarity. Additionally, the impact of informativeness on website familiarity is stronger for travelers who identify as younger than their chronological age. Moreover, older travelers' familiarity with a website improves their revisit intention. The current study found not only significant travel website atmosphere factors to boost older travelers' participation in online tourism platforms but also significant older travelers' groups depending on their cognitive age perception to magnify the effect of website atmosphere.