JSFiddle - React, Tailwind, and code Playground

JavaScript

function getAge(dateString) {
  var now = new Date();
  var today = new Date(now.getYear(),now.getMonth(),now.getDate());

  var yearNow = now.getYear();
  var monthNow = now.getMonth();
  var dateNow = now.getDate();

  var dob = new Date(dateString);

  var yearDob = dob.getYear();
  var monthDob = dob.getMonth();
  var dateDob = dob.getDate();
  var age = {};
  var ageString = "";
  var yearString = "";
  var monthString = "";
  var dayString = "";


  yearAge = yearNow - yearDob;

  if (monthNow >= monthDob)
    var monthAge = monthNow - monthDob;
  else {
    yearAge--;
    var monthAge = 12 + monthNow -monthDob;
  }

  if (dateNow >= dateDob)
    var dateAge = dateNow - dateDob;
  else {
    monthAge--;
    var dateAge = 31 + dateNow - dateDob;

    if (monthAge < 0) {
      monthAge = 11;
      yearAge--;
    }
  }

  age = {
      years: yearAge,
      months: monthAge,
      days: dateAge
      };

  //if ( age.years > 1 ) yearString = " years";
  //else yearString = " year";
  var totMonths = age.months + age.years;
  if ( totMonths > 1 ) monthString = " months";
  else monthString = " month";
  if ( age.days > 1 ) dayString = " days";
  else dayString = " day";

	if ( (totMonths == 0) && (age.days > 0)
  	ageString = "Only " + age.days + dayString + " old!";
  else if ( (totMonths > 0) && (age.days == 0))
  	ageString = totMonths + monthString + " old.";
  else if ( (totMonths > 0) && (age.days > 0))
  	ageString = totMonths + monthsString + " and " + age.days + dayString + " old.";
  else ageString = "Oops! Could not calculate age!";

  return ageString;
}


alert(getAge('11/27/1993'));