I am a little confused as to understanding this gemarah.
לא עשו בו קטן כגדול אמר רב לא עשו ביאת פחות מבן תשע שנים כבן תשע שנים ושמואל אמר לא עשו ביאת פחות מבן שלש שנים כבן שלש שנים The Gemara asks: What does it mean that the Torah does not deem a younger boy to be like an older boy? Rav says: It means that the Torah does not deem the intercourse of one who is less than nine years old to be like the intercourse of one who is at least nine years old, as for a male’s act of intercourse to have the legal status of full-fledged intercourse the minimum age is nine years. And Shmuel says: The Torah does not deem the intercourse of a child who is less than three years old to be like that of one who is three years old.
So from there I understand that once a man is 9 years old (or three years old according to Shmuel), if he performs homosexual acts he is liable to death. Fine. But the next verse states:
במאי קמיפלגי רב סבר כל דאיתיה בשוכב איתיה בנשכב וכל דליתיה בשוכב ליתיה בנשכב The Gemara asks: With regard to what principle do Rav and Shmuel disagree? The Gemara answers: Rav holds that any halakha that applies to one who engages in intercourse actively applies to one who engages in intercourse passively, and any halakha that does not apply to one who engages in intercourse actively does not apply to one who engages in intercourse passively. Therefore, just as one who engages in intercourse actively is not liable if he is less than nine years old, as the intercourse of such a child does not have the halakhic status of intercourse, so too, if a child who is less than nine years old engages in homosexual intercourse passively, the one who engages in intercourse with him is not liable.
Why is someone who is over the age of 9 not liable for death for these acts to someone less than 9? I see Rashi refernces Nidda 45a which says that intercourse with somone less than three is like a finger to the eye but I don't understand what that means, an explanation would help. Also, what is the punishment for the active person instead?