Don’t worry, there are a lot of grey beards (shaven or not) on this forum.
RS274D is ancient. RS274X is also getting old. KiCad currently defaults to the X2 version of the Gerber format.
What is your intention with these old files? Why do you want to open them with KiCad’s gerber viewer in the first place? Do you want to Reverse engineering KiCad project from Gerber files ?
KiCad does have importers for schematics and PCB’s for a bunch of different programs (and those are being extended slowly) Circuitmaker is among those, but probably only a newer version. Maybe it’s an option to first convert your files to a newer circuitmaker version, and then import your old projects into KiCad.