I was able to light the pilot light and it stays lit, but when I flip the switch to turn on the gas nothing happens.

Is this a new situation with an old install or did you just install now? Which brand?

13 year old... worked last year. Turned off pilot for summer. Pilot is on, but the switch will not turn on the main burners. Checked wiring and it is good.

Is the pilot controlled by a thermocouple or a thermopile? You may not be producing enough millivolts to allow the main burner to open if you have a weak thermopile.

No switch on mine, after the pilot lights I must turn a knob 1/4 turn to allow flame to light. Is your different, no knob to turn

Mine is like that. Has a lit pilot with a 120 VAC wall switch. Flip the switch and it's on. Can adjust under front access panel for flame height. New house (4 yrs) , Majestic direct vent glass front set. The set in our mountain house is as you described, 1/4 turn to left. .