title: MongoDB all entries with maximum values in column
body: <p>I have the data</p>
  
  <pre><code>{"name" : "user1", age : 40 }
  {"name" : "user2", age : 45 }
  {"name" : "user3", age : 50 }
  {"name" : "user4", age : 40 }
  {"name" : "user5", age : 40 }
  {"name" : "user6", age : 21 }
  </code></pre>
  
  <p>I want all rows having the maximum age.</p>
  
  <p>Basically fetch all rows whose column value is maximum in the column. </p>
  
  <p>SQL query : <code>SELECT * FROM Person WHERE age = (SELECT max(age) FROM Person)</code></p>
  
  <p>How can I do the same in MongoDB ? Thank you</p>