Loop that prompts user until valid input

Question: How to continuously prompt user when age is invalid (below 0 above 200, or not-a-number)?

var userAge = prompt("Please enter your age");
while (isNaN(userAge)){
alert("That's not a number, please retry.");
var userAge = prompt("Please re-enter your age.");
}
if (userAge == 0){

alert("So you're a baby!");
}
while( userAge < 0  || userAge >= 200){

alert("I think you may be lying about your age.");
var userAge = prompt("Please re-enter your age, don't lie this time.");
{continue}
}if (userAge > 0 || userAge < 200){

alert("That's a good age."); 
}

</script>