Re: Minimum font size requirement or guideline for accessbility

It is absolutely right, when it comes to the CSS, to say don't use px
units. But using CSS "medium" is also bad as that still overrides the user
settings. Either use rem and em, or %, because then the sizing is based on
the user's own font size they selected in their operating system or browser
settings. Some users choose a larger font size than the preset one, and
don't want the developer overruling that!

However, leaving all that aside, the original question was "...wondering if
there are any requirements or guidelines for font size that will help
better readability for all". The answer to that you do need a minimum, or
even people with good vision will find it tiring to read lots of text in a
small font. All those websites using 12 or even 10px are a bit too small
for comfort for most people. So it seems to be generally recommended (but
nothing for this in the WCAG) that 16px (talking here in CSS terms of px
units not pixels), which equates to CSS "medium" in most browsers, is
really as small as a design should ideally go. But just saying "don't go
below medium font" just begs the question, What do you mean by medium!