Count of age to convert to 1 year, when it's 6 motnhs

I am looking for a solution on how to update the script, so that it would give me a value of 1, when it is equal to 6 months. If the value is less than 6 months, to have 0. Also, I do not know how to make that the field would allow saving fixed value.

Here is the script I am using in 'Custom Calculation' box:

event.value = "";

var dobValue = getField("Textfield-49").value;

if (dobValue!="") {

var dob = util.scand("dd/mm/yyyy", dobValue);

var today = new Date();

var age = today.getTime() - dob.getTime();

// compute age in milliseconds

var nAgeMilliseconds = today.getTime() - dob.getTime();

var nAgeYears = ( age / (1000 * 60 * 60 * 24 * 365.2425) - 0.005);

event.value = Math.floor(nAgeYears);

}