title: How to get difference in years from current date and Ecto.Date instance
body: <p>Let's say I have a <code>Person</code> model and each person has a birthday field set as an <code>Ecto.Date</code> column. </p>
  
  <p>So if I retrieve a record from the database which represents an instance of this model, what is the best way to get this person's age from his <code>birthday</code> column?</p>