I have a Merauke blue tongue for over a year now. When they get around this age, shedding slows down from a few times a month as a baby to once every other month. Mine started to shed every other month since December.
You don't really need a scale like you do with snakes to confirm if they are overweight or not. Really easy to tell for BTSis if they look more rectangular in the body, it is time to cut back the feedings. A good weight will show acute oval shape, from neck to tail. It is hard to get them to lose the weight so starting the diet early helps.
I would suggest at this age to cut back feeding its meal once a week. You can give it veggie treats if it will take it without meat throughout the week or snails if you have them. Mostly veggies to meat ratio like bearded dragons. Your BTS will always act like it is hungry, don't worry, it won't starve itself. In fact, they can go without food for weeks or even months. The meal portion should be no bigger than the size of its head, but since veggies have no calories, feel free to give as much as he will take.