Knowing that you found the font size in the website small, I suspect that you are finding the font in the forum too small as well. I am a little surprised that when we increased the size of the font for the site that that did not alter the size in this forum.
It turns out that there are two ways to increase the font size in bbPress.
One is with a site plugin that is leased at $19/year. (I don’t want to do that.)
The other is to alter the related css file. That code change is simple enough, but will vanish the first time this theme is updated (which is likely to happen every few months). The remedy for this is to create a child theme, and make the css edit in the child theme. This is probably something we’ll want to do eventually, so I’ll put it on my todo list. But, unless you see this as something urgent, I’ll leave the child theme for a quieter time.