No reason to worry. And a perfect example of why you shouldn't believe just one source unless you know that source to be reputable. They shed when they need to shed, and there are variables which contribute to when they shed. They shed more often as juveniles because they are growing more quickly, but there is certainly no reason to worry if they don't shed every month. Just for reference, my juvenile boy, Tyson, has shed six times since I got him in January. Sheds were anywhere between 5 and 8 weeks apart and he is a perfectly healthy snake.