There are lots of plugins available that will add a message box to the top of your posts if it’s above a certain age – e.g. 2 years old. However, I had a very specific requirement. After updating my site recently, I had to make changes to my posts to get them to fit with the new design. However, with over 1000 posts, it was going to be a long, long job to do them all. So I didn’t. I only did 2013 onwards. So, I wanted to display an appropriate message for any posts old than that – a set date rather than a moving time period.