Return the age given the parameters

getAge.js

function getAge(month, day, year) {
  const birthDate = new Date(year, month - 1, day)
  const fromNow = new Date() - birthDate

  const absoluteAge = new Date(fromNow).getFullYear()

  // that's because timestamps starts from 1970, so
  // we're getting relatively to that year
  return Math.abs(absoluteAge - 1970)
}