The answer is yes. Immatures peregrines have some differences in plumage from their parents. When young peregrines fledge from the nest they are as big as they are going to get. If you are seeing different sizes, remember that is the difference between male and female, not adult and immature. One main difference between the parents and young is in their color and pattern of coloration.
Young peregrines are a dark brown on the back and head.
The adults are a dark blue-black on the back and head. Their belly is covered with light horizontal barring. All peregrines, no matter what age, have a wide malar stripe on each side of the head. The picture here is of an immature falcon. Sometimes it is difficult to identify birds.