script.js

let userInput = document.getElementById('date');
userInput.max = new Date().toISOString().split("T")[0];
let age = document.getElementById('age')
function calculateAge() {
	let birthDate =  new Date(userInput.value);


	let d1 = birthDate.getDate();
	let m1 = birthDate.getMonth() + 1;
	let y1 = birthDate.getFullYear();

	let toDay = new Date();

    let d2 = toDay.getDate();
	let m2 = toDay.getMonth() + 1;
	let y2 = toDay.getFullYear();


let d3, m3 , y3;

y3 = y2 - y1;

if (m2 >= m1) {
	m3 = m2 - m1;
}else{
	y3--;
	m3 = 12 + m2 - m1
}

if (d2 >= d1) {
	d3  = d2 - d1;
}else{
m3--;
d3 = getDaysinMonth(y1 , m1) + d2 - d1;
}
if (m3 < 0) {
	m3 = 11;
	y3 --;
}

if (isNaN(y3) || isNaN(m3) || isNaN(d3)) {
    age.innerHTML = `Please enter valid date.`;
  } else {
    age.innerHTML = `You are ${y3} years, ${m3} months, and ${d3} days old`;
  }
}

function getDaysinMonth (year , month) {
   return new Date(year , month , 0).getDate();
}