Do you access to your theme’s functions file?
Yep, I’ve got complete access over the whole website and hosting.
In which case this is the easiest way.
create a directory on your theme called ‘bbpress’
where %your-theme-name% is the name of your theme
Make a copy of this file, and put in in the directory called bbpress that you created above, so you end up with
bbPress will now use this template instead of the original
and you can amend this
so go to line 60 which says
<span class="bbp-topic-started-by"><?php printf( __( 'Started by: %1$s', 'bbpress' ), bbp_get_topic_author_link( array( 'size' => '14' ) ) ); ?></span>
and change the ‘size’ => ’14’ to a larger number for instance ‘size’ => ’20’
Instead of going through each template and possibly changing this, you can also use a php code function listed int this topic.
The original source of their code seems to be from this guide.