Sometimes, especially in babies, it can be hard to tell when they are going to shed. Sometimes I will feed a baby in the morning, come back at noon and suddenly they look milky and are starting to shed, and by that afternoon they are totally finished. So they don't always look whitish for days prior. But you should see skin sprinkled everywhere, they can be pretty messy.
They shed as they grow, obviously, so not shedding might mean that your guy might just not be growing super quickly. Which is not in and of itself a bad thing, different animals grow at different rates for no reason. I've had panther shed every 2-3 weeks as they grew like weeks and others who would go 2 months between sheds.
But it's never a bad thing to double check what you're doing (Feeding enough? Gutloading well? Supplements correct? Enough misting and humidity? etc.) to make sure everything is as well as it should be, though.