Gmail is one of the most popular and widely used email services in the world. It offers many features and benefits to its users, such as unlimited storage, spam protection, and integration with other Google products. However, sometimes Gmail users may encounter some problems or errors when creating or using their accounts. One of these errors is the message Please enter a valid birthday that appears when you try to enter or change your birthday on Gmail. This error can prevent you from signing up for Gmail or accessing your account. In this article, we will explain what this error means, why it happens, and how to fix it.