{% assign post = include.post %}
{% assign postSecs = post.date | date: '%s' %}
{% assign nowSecs = 'now' | date: '%s' %}
{% assign ageSecs = nowSecs | minus: postSecs %}

{% unless post.tags contains "evergreen" %}
  {% comment%} Two years in seconds {% endcomment %}
  {% comment %} TODO: more dynamic age? i.e. "three years ago" or "five years ago", etc.? {% endcomment %}
  {% if ageSecs > 63072000 %}
    <aside class="outdated">
      <strong>Note:</strong> this post was written over two years ago. The information below may be outdated.
    </aside>
  {% endif %}
{% endunless %}