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

{% if page.date|date('U') < 'now'|date_modify('-12 months')|date('U') %}
    <div class="border-2 border-blue p-4 mb-6">
        <p class="text-sm mb-0">
            <span class="font-bold">Warning:</span>
            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 I don't always update old posts with new information, so some of this information may be out of date.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 %}