This is the solution to the Codewars Kata: How Old Will I be in 2099

KATA: How Old Will I Be In 2099?

function  calculateAge(birthDate, otherDate) {

var age = otherDate - birthDate;

  if(age === 1) {
  return 'You are ' + age + ' year old.';
    } else if(age > 1) {
      return 'You are ' + age + ' years old.';
    } else if (age < -1) {
      return 'You will be born in ' +  Math.abs(age) + ' years.';
    } else if (age === -1) {
      return 'You will be born in ' + Math.abs(age) + ' year.';
    } else {
      return 'You were born this very year!';
    }
}