ValidateAge.js

function validatateAgeBelow18 (value){
  // value is the user chosen date
  // get today's date
  var todaysDate = Date.now()
  var todaysDateInSeconds = Math.floor(todaysDate/1000);
  console.log("todaysdate", todaysDateInSeconds);
  // convert to epoch time
  // comvert to seconds.
  // get date user choose
  var userDate = value;
  var userDateInEpochTime = Date.parse(userDate);
  // console.log("userdate", userDateInEpochTime);
  var userDateInEpochTimeInSeconds = Math.floor(userDateInEpochTime/1000);
  console.log("userdate", userDateInEpochTimeInSeconds);
  // console.log("userdate", userDateInEpochTime);
  // convert to epoch time and seconds
  // subtract user date from todays date
  var diffInAge = todaysDateInSeconds - userDateInEpochTimeInSeconds;
  console.log("diffInage", diffInAge );
  var _18YearsInS = 567648000;
  // check if it is less than 18 years.
  var isUserOlder18 = diffInAge > _18YearsInS
  console.log(isUserOlder18)
  // if so, return an error that the age cannot be less 18
  // if above 18, the validator returns no erros
}

validateAgeBelow18(2021-01-05)