Age: <input type="text" id="age" />
<br/>
<!--
radio boxes can only have one control checked; make sure that name is the same for all radio controls; id must be different; set default by adding "checked"
-->
<input type="radio" name="sex" id="male" value="man">Male<br/>
<input type="radio" name="sex" id="female" value="woman">Female<br/>
<input type="radio" name="sex" id="unknown" value="other" checked>Unknown
<p />
<button onClick="processForm()">Check Age</button>

<script>
function processForm()
{
  var male= document.getElementById("male").checked;
  var female= document.getElementById("female").checked;
  var unknown= document.getElementById("unknown").checked;
  var gender = "";

  if (male == true)
  {
    gender = "male";
  } else if (female == true) {
    gender = "female";
  } else {
    gender = "unknown";
  }

  alert("Gender: " + gender);

} // end processForm
</script>