It’s quite normal for some dogs to scoff their food without chewing. If he is not gagging then it’s a good indicator it’s ok. There are dog bowls designed for slower eating available in most pet stores. They work by having an irregular design that makes it more difficult to get at food.
He is hungry and growing. The presence of other dogs would also be an incentive to make him scoff his food more quickly.
There are a few suggestions:
A good way to get a dog to eat more and more quickly is to feed the dog in the presence of another dog. So the reverse can also work.
If your puppy, is most likely being fed more frequently than your older dogs. I would suggest putting him in a place away from the other dogs when feeding him. Either feed him in the kitchen where you are, with the other dogs in another room or outside. Or the other way around. Preferably where he cannot see the other dogs while he is eating.
Another thing is to provide some suitably sized raw meaty bones. This will help keep him occupied and alleviate his need to scoff, as he will have the sensation of chewing and tasting for a prolonged period.
The issue with this is, in a more than 1 dog household, is that he may need to be separated from the other dogs, as fights can possibly break out with unsupervised bones. Or you can feed your other dogs larger bones, but it can still become a recourse guarding battle and I suggest supervising this and collecting unfinished bones from laying around or out in the garden.
The other thing you can do is feed him more frequently (though four feeds is ideal) and/or increase his food. His weight gain may be looking healthy, but he may genuinely be hungry and require more food. It’s important to incrementally increase a puppy’s total daily food allowance as he grows.
If you want to increase the amount of frequency of feeding, you can create a couple of treat meal times, where the food is not presented in the same way as his usual pattern. Give him something with high protein and fat, like a fatty bony off-cut of meat.
That is a suitable size that he can crunch it all up and eat it all. Brisket bones can be really good for this. While recommending some fatty treats for a rapidly growing puppy, it is not something I’d routinely recommend for an adult dog.
You can also try wetting the food; it will go down easier.