I think there may be a couple of other reasons for the change in font size in addition to those listed. I don't think it's necessarily age related.
Previously web designers were in complete control. In my experience, we do more user testing now, which means that designers get to hear feedback such as "I can barely read that article" or "My sight's not perfect so, it might take me a minute to find...", etc.
I also think we're much more aware of 'accessibility' issues than we were a few years ago. With WCAG 2.0, Section 508, AODA, etc., many organizations now have to comply with mandatory accessibility legislation. While this doesn't dictate a minimum font size, I think designers are more apt to consider the needs of their audience above the aesthetics of the site.