Obtenha a idade usando o momento
var a = moment();
var b = moment('{dem_pat_birthyear}', 'YYYY');
var diff = a.diff(b, 'years'); // calculates patient's age in years
diff; // this prints out the age
//In this calculation {dem_pat_birthyear}
//needs to be replaced with your variable name for birth year.
Vivacious Vendace