Display dates of the earliest and the latest posts in each subcategory

So I will reply to my post myself.

Not so much researching and reading The Codex led me to the following result:

<?php
$args = array('parent' => XX, 'orderby' => 'ID', 'order' => 'desc');
$categories = get_categories( $args );
foreach  ($categories as $category) {
	echo '<p><strong><a href="' . get_category_link( $category->term_id ) . '" title="' . sprintf( __( "%s" ), $category->name ) . '" ' . '>' . $category->name.'</a></strong>';
	if ( $cat_desc = $category->description ) echo '<br />'. $cat_desc .''; else echo '';
	echo '<br />Posts in this subcategory: '. $category->count .''. $comments .'';
	foreach (get_posts('cat='.$category->term_id.'&order=asc&orderby=date&posts_per_page=1') as $post) {
		setup_postdata( $post );
		echo '<br />'.get_the_date('j F Y').': <a href="'.get_permalink($post->ID).'">'.get_the_title().'</a>';
	}
	echo '</p>';

// for the FIRST variant

	foreach (get_posts('cat='.$category->term_id.'&order=asc&orderby=date&posts_per_page=1') as $post) {
		setup_postdata( $post );
		echo 'Active since '.get_the_date();
	}
	foreach (get_posts('cat='.$category->term_id.'&order=desc&orderby=date&posts_per_page=1') as $post) {
		setup_postdata( $post );
		echo ' till '.get_the_date();
	}

// and for the SECOND variant

	foreach (get_posts('cat='.$category->term_id.'&order=asc&orderby=date&posts_per_page=1') as $post) {
		setup_postdata( $post );
		echo 'Years active: '.get_the_date(Y);
	}
	foreach (get_posts('cat='.$category->term_id.'&order=desc&orderby=date&posts_per_page=1') as $post) {
		setup_postdata( $post );
		echo '-'.get_the_date(Y);
	}
}
?>

You may also list some or all (by adding the number which is surely larger than maximum imaginable number of posts into appropriate variable) posts in each subcategory by including the following snippet:

	foreach (get_posts('cat='.$category->term_id.'&order=desc&orderby=date&posts_per_page=1') as $post) {
		setup_postdata( $post );
		echo '<br />'.get_the_date('j F Y').': <a href="'.get_permalink($post->ID).'">'.get_the_title().'</a>';
	}

Mind the variables.

As it is almost my first experience in PHP coding the result might appear not so elegant as it could be. But it works.