title: Setting an expiry date or a maximum age in the HTTP headers
body: <p>I just finished a website that I designated and submitted it to google insights 
  <a href="http://developers.google.com/speed/pagespeed/insights/" rel="nofollow noreferrer">http://developers.google.com/speed/pagespeed/insights/</a>
  for performance reviews, and this is the result I got. <img src="https://i.stack.imgur.com/qjcMD.png" alt="enter image description here"></p>
  
  <p>It says, I need to set expiry date or a maximum age in the the HTTP headers, but I don't know how it is possible to set expiry date for anything other than cookies/sessions.</p>