Beardies can vary considerably in size, from four months to a year old, so yours is not too big, or too small. It is normal for them to eat like piggies!! So, let him! As you do, keep offering him salad daily, but it is not unusual for them to prefer live protien while less than a year old, due to the spectacular growth rate. I would offer a good variety of live protiens. I offer mine superworms, mealworms, waxworms, in that order, every day. Always, I offer crickets. I would dust them with calcium/vit. D powder every day, until he is over his fast growth period (usually, about a year old, but again, it varies) and also a general vitamin supplement made especially for reptiles,a few times a week. If you would like recommendations, contact me. At his age, and at the fast growth rate, it is super important to be sure they are getting plenty of good nutrition, heat for metabolizing and digestion, and UVB for bone growth. If needed, there is plenty of info about that on this site.
I have no experience with feeding BSFL, but I remember that at that age, my boy ate an astonishing amount of crickets and worms. With live food, the general rule is, do not feed anything that would not fit in the space between the eyes of your Beardie. They can choke on larger prey, and also they have a gag reflex that can be triggered, and larger food is a danger to them. But, with his appetite, bigger food than what you are feeding may be something to consider.
There is some controversy about superworms being too big, etc, but I have never had a problem. Waxworms, while generally loved by Dragons, are so full of fat, they are like us eating a candy bar:good for quick energy, but not good, as a regular diet source. I offer them as a treat, only. They are good to tempt a Beardie who is ill and has lost his appetite. Sounds as if your boy does not have that particular problem!
What is your Beardies name? Can you send a photo? (the only thing as good to us as looking at our own Beardies photos, is to look at everyone elses Beardies photos!??)
My big boy is three years old, adorable, and a full two feet long. I love every inch of him!
Here is DeziLu, saying "welcome to our wonderful site!"