JSFiddle - React, Tailwind, and code Playground

HTML

<input type="date" style="width:210px" name="txtdateofbirth" onChange="calage(this.value)" id="txtdateofbirth"><br />Age : <span id="txtage"></span>

JavaScript

function calage(dob) {
    var date1 = new Date();
    var y = date1.getFullYear();
    var by = dob.split("-", 1);
    var age = y - by;
    $("#txtage").html(age);
}