Vaejovis spinigerus growth rate?

i have some 4-5th instar V. spinigerus had them for many months now and none of them have molted once! i was told that they grow fast..i'm keeping them in small deli cups and on dry coco fiber. giving water once or twice a month and feeding a small cricket once a month or so [because the crix i give them are about the same size as they are...]. so any tips on how to help them grow faster? also, should i be feeding them more often?

id say warmer enviroment and multiple smaller meals.

I'd feed them at least once a week until they refuse to eat any more. I feed instars twice a week. Try bumping the temperature up to 85 F if it's not already there.