Age Calculator App with DOM Manipulation using Vanilla JavaScript

My first time dealing with heavy JavaScript. Though I covered everything from validating each input field, blank fields to even checking for if the given date actually exists such as 31 April, 1991 which is a valid format but invalid date. After tackling all the issues, I believe my code looks a bit bloated and swarmed with functions. Any feedback regarding best practices and optimization from the more senior developers will be well appreciated. The final product is approximation and there's a chance of it being off a day or 2 which isn't too chaotic but keep in mind if the date is nearing end of month or year, it could make a lot of difference.