The Gamara tells us that rav Chisdah asked Rav Hunah what is the din if the rebbi need his talmid Rav Hunah thought that rav Chisdah was hinting that Rav Hunah needed rav Chisdah and he was up set at him for forty years. the GM continues and says that both rav hunah and rav chisdah fasted fourty days since they realized that they made a mistake.
Question: if they realized that they made a mistake and fasted 40 days why were they upset for 40 years after the 40 days they should have made up.
M. Friederwitzer, Yerushalayim
Both Rabeinu Chananel and Rabeinu Peretz (in the Shitah Mekubetzes) read the Gemara differently than you did. The way the read it, Rav Huna told Rav Chisda that until Rav Chisda is 40 years old, he still needs his Rebbi, Rav Huna, as we find in Avodah Zarah that a Talmid doesn't fully understand the teachings of his Rebbi until the Talmid is 40 years old. This obviously answers your question. (The Maharsha and Toras Chaim may have read it the way you did.)
Best regards, Mordecai Kornfeld