Re-add text above old post content

source/_layouts/post.html.twig

@@ -5,10 +5,16 @@
         <div class="space-y-6">
             <header>
                 <time datetime="{{ page.date|date('Y-m-d') }}">
-                    {{- page.date|date('jS F Y') -}}
+                    Posted on {{ page.date|date('jS F Y') -}}
                 </time>
             </header>
 
+            <div>
+                {% include 'post/old-post-message' with {
+                    post: page,
+                } only %}
+            </div>
+
             <div class="markdown">
                 {{ parent() }}
             </div>

source/_partials/post/old-post-message.html.twig

@@ -0,0 +1,12 @@
+{% macro shouldDisplayOldPostMessage(post) %}
+    {% set cutOffDate = 'today -1 year'|date('U') %}
+    {{ post.date <= cutOffDate }}
+{% endmacro %}
+
+{% import _self as helpers %}
+
+{% if helpers.shouldDisplayOldPostMessage(post)|trim %}
+      <div class="p-6 my-10 border border-gray-300 dark:bg-gray-800 dark:border-gray-700">
+          <p><strong>Warning:</strong> This post is over a year old. I don't always update old posts with new information, so some of this information may be out of date.</p>
+      </div>
+{% endif %}