This is the script to calculate age in Adobe Acrobat Pro.
This works but throws a internal error.
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// Calculate Age
// Ref: https://community.adobe.com/t5/acrobat-sdk-discussions/how-to-override-a-calculation-with-manual-entry-in-results-field/td-p/10856126
console.println("Calc Age Started");
var dobValue = getField("DOB").value;
if (dobValue!="") {
var dob = util.scand("mm/dd/yyyy", dobValue);
var today = new Date();
// compute years on full year only
var AgeCalulated = today.getFullYear() - dob.getFullYear();
// adjust for months before month of birth
if (today.getMonth() < dob.getMonth()) AgeCalulated = AgeCalulated - 1;
// adjust for today's month equal to dob's month and today's date before the date of birth
if ((today.getMonth() == dob.getMonth()) && (today.getDate() < dob.getDate())) AgeCalulated -= 1;
//event.value = AgeCalulated;
console.println("Calc Age Proceess Start");
getField("AGE").value=AgeCalulated;
console.println("Calc Age Proceess Finished");
}