CurrentAge Function Not Giving Appropriate Output

I'm fairly new to writing script and so can only assume I have got something incorrect because the 'ages' are failing to change by -1 when the month and day is greater than the current date.

function currentAge(value){
var theDOB = value;
var theDOB = theDOB.split('/');
var DOBday = theDOB[0];
var DOBmonth = theDOB[1];
var DOByear = theDOB[2];

var todaysDate = new Date()
var yr = todaysDate.getFullYear();
var mth = todaysDate.getMonth() +1;
var dayy = todaysDate.getDate() +1;
var theAge = (yr -DOByear);
var yearBefore = (theAge -1);

if (mth <= DOBmonth && dayy < DOBday) {
return yearBefore;
}
else {
return theAge;
}}