Untitled

// Input the birthdate from any layer, text, comp name etc. (mm, dd, yyyy)
var birthDateUnfortmatted = thisComp.layer("Date of Birth").text.sourceText;

// Get todays date
var today = new Date(); 

//Split the input into its parts to rearrange later 
var birthDateParts = birthDateUnfortmatted.split(/[/]/);
var month = birthDateParts[0]-1;
var day = birthDateParts[1];
var year = birthDateParts[2];

// Format the birthdate (yyyy, mm, dd)
var birthDate = new Date(year, month, day); 

// Subtract the birth year from todays years
var age = today.getFullYear() - birthDate.getFullYear(); 

// Check if the month has already been reached/passed
var m = today.getMonth() - birthDate.getMonth(); 

// Check if the birthday has already been reached/passed
var d = today.getDate() - birthDate.getDate(); 


if(m == 0)
	if(d < 0)
		age -1;
	else
		age;	
else
	if (m < 0) 
		age-1;
	else
		age;