title: Min/Max of object.attribute in a list of object with guava
body: <p>Let's take a list of <code>Person</code> defined as </p>
  
  <ul>
  <li>Name</li>
  <li>Surname</li>
  <li>Age</li>
  </ul>
  
  <p>I want the max(age) in a <code>List&lt;Person&gt;</code>.</p>
  
  <p>I could iterate on this list and manually keep the max :</p>
  
  <pre><code>Integer max = null;
  for(Person p : list) {
    if(max == null || max &lt; p.getAge()) {
      max = p.getAge();
    }
    return max;
  }
  </code></pre>
  
  <p>But I feel that there might exist a combination of Guava methods which can do it for me. If I write a <code>Function&lt;Person, Integer&gt;</code>, is there a ready-to-use method to get the max from the list?</p>