Add utility function (calculate age in range)

src/interfaces/utils.ts

@@ -0,0 +1,19 @@
+export function calculateAge(start: Date, end = new Date()) {
+  if (start.getTime() > end.getTime()) return;
+
+  let year = end.getFullYear() - start.getFullYear();
+  let month = end.getMonth() - start.getMonth();
+  let day = end.getDate() - start.getDate();
+
+  if (month < 0) year -= 1;
+  if (month < 0) month += 12;
+  if (day < 0) {
+    month -= 1;
+    day =
+      new Date(start.getFullYear(), start.getMonth(), 0).getDate() -
+      start.getDate() +
+      end.getDate();
+  }
+
+  return { year, month, day };
+}