Is there a standard method to make the gedit font size larger?
You can change the font size from the application itself, Text Editor ==> Preferences ==> Font and color and adjust the size and font as desired. Or you can use gsettings.
#Get the font and size gsettings get org.gnome.desktop.interface monospace-font-name
#Set the font and size gsettings set org.gnome.desktop.interface monospace-font-name 'monospace 15'
Let me know if this helps.