"And an uncircumcised male" (Genesis 17:14): from the place where he is male, there he is uncircumcised. From here [we learn] concerning circumcision that in that same place he circumcises the flesh of his foreskin. And he is not liable to karet [excision] except for the male himself, "who has not circumcised the flesh of his foreskin," when he has grown up; but his father or the court are not liable to karet on his account.
Who Bears Karet for an Uncircumcised Male
Midrash Aggadah, Genesis 17:14
וערל זכר. ממקום שהוא זכר הוא ערל, מיכן למילה שבאותו מקום ימול בשר ערלתו, ואינו חייב כרת אלא הזכר אשר לא ימול בשר ערלתו כשיהיה גדול, אבל אביו או בית דין אינן חייבים עליו כרת: