Font Size

There's no master setting within Appian that I happen to be aware of, however I can vouch that Appian plays rather nicely with different browser zoom levels - in other words, if there are users who'd prefer larger writing, they could try setting their zoom level to something greater than 100% and things should still look pretty nice.

Note: if you're an expert at creating/using custom fonts, the Admin Console does include a feature now to add custom font files for use on particular sites - I assume that it could be supplied with a font file where all the default sizes are a little bigger than usual.  However this will be out of technical reach of a lot of people, even including appian developers (and I personally haven't used this feature yet so I don't happen to know how much work would really be involved).  Maybe some others here will have already experimented with this and could provide more detailed feedback.