If "he" is 16-18 weeks old, that's a she! Hard to tell when wet, but I don't see any pointy sickle or hackle feathers on there. Just a girl who will probably start to lay in a month or so! If that was a roo, I would expect a larger deep red comb by now.
Here are pictures of single comb girls who are mature and laying. I'm going to say your girls comb there will grow some more before point of lay. I'll be darned if it is a roo, but I don't think so if they all look like the ones in the pic of the flock.
Even this is a girl's comb that is mature, albet, it is a leghorn, known for big floppy combs:
As rooster leghorn combs look like the following by 20 weeks old:
However... if your "he" is only like 8-10 weeks old.. it could be a he.... so age can make a pretty big difference. Note the feathers on the roosters neck there, they are kind of pointy. If you find "pointy" feathers on the girls, it is likly they are actually boys. Girls don't have "pointy" feathers.
On this rooster, you can see around the neck and by the "saddle" near the tail, the feathers are long and pointy, hanging down, if you have boys, they will eventually start to grow those in, and if are 4 months old, should be visable by now if they are male.
About feather growth speed...My hen who went completely bald due to moult, has about half her feathers back two weeks later. She literally was a pin cushion. Lost 90%, literally 90% of her feathers in 3 days, and within 10 days, each had opened up and started being a feather again. With proper nutrition and extra protein, feathers do grow back quickly. Of course, it does vary between birds.
Here are pictures of single comb girls who are mature and laying. I'm going to say your girls comb there will grow some more before point of lay. I'll be darned if it is a roo, but I don't think so if they all look like the ones in the pic of the flock.

Even this is a girl's comb that is mature, albet, it is a leghorn, known for big floppy combs:

As rooster leghorn combs look like the following by 20 weeks old:

However... if your "he" is only like 8-10 weeks old.. it could be a he.... so age can make a pretty big difference. Note the feathers on the roosters neck there, they are kind of pointy. If you find "pointy" feathers on the girls, it is likly they are actually boys. Girls don't have "pointy" feathers.
On this rooster, you can see around the neck and by the "saddle" near the tail, the feathers are long and pointy, hanging down, if you have boys, they will eventually start to grow those in, and if are 4 months old, should be visable by now if they are male.
About feather growth speed...My hen who went completely bald due to moult, has about half her feathers back two weeks later. She literally was a pin cushion. Lost 90%, literally 90% of her feathers in 3 days, and within 10 days, each had opened up and started being a feather again. With proper nutrition and extra protein, feathers do grow back quickly. Of course, it does vary between birds.