Why does Jonas feel his childhood is slipping away from him?

Jonas feels his childhood slipping away from him because he is growing up and realizing the complexities and responsibilities of the world around him. As he gains a deeper understanding of his role as the Receiver of Memory, he starts to see the innocence and simplicity of childhood fading as he confronts difficult truths. additionally, he begins to feel disconnected from his peers who are not privy to the knowledge and experiences he is gaining.