findIndex (JavaScript Array Method)

const tnwAges = [19, 39, 28, 43, 29, 45, 53];

function tnwFun1(){
    document.getElementById("demo").innerHTML = tnwAges.join("
");
}

function tnwFun2(){
    document.getElementById("demo").innerHTML = tnwAges.findIndex(chkAge);
}

function chkAge(age){
    return age > document.getElementById("myAge").value;
}

To see video in YouTube.