I found a solution on my Mac Book Pro. It is kind a kludge but it works. Changing the font directly in the Font Size selection window does not work. It always reverts back to 12 pts. However, when I increase the font percentage in each individual selection in the middle of the preferences selection window it increases the font size and remains. To get a comfortable font size, I have to use the maximum increase of +39 %.
It works and Inform 7 is incredible software. I have been experimenting with Twine and Tads 3 as well. Inform 7 is the perfect balance and has the complexity and flexibility I am looking for.
I will install the Windows 7 version on an old Dell laptop to see if the font size can be changed normally there.
Thank you for all of your help!