You have very healthy looking goldfish and a nice aquarium setup from the pictures. Congrats
For most speciments, the cap or head growth will not appear until around the 2nd year. Once the growth appears it will not stop growing until the fish is a little over three years of age. However in some cases, the head growth will appear as early as a year. Since your goldfish are still so young, i doubt any of them has any head growth yet.