Tosfos s.v. Pashit writes that the Rashbam is of the opinion that Rav Achai mentioned in the Gemara here is Rav Achai Gaon, the author of the Sheiltos. For this reason Rav Achai employs unique terminology throughout the Talmud. Examples of the unique terminologies are parich Rav Achai, parish Rav Acahai. Rabbeinu Tam, however, disagrees with the Rashbam, because Rav Ashi is the one who responds to Rav Achai. Rabbeinu Tam apparently understood that Rav Ashi and Rav Acahai did not live in the same era.
I was wondering if it was possible to say in defense of the Rashbam that Rav Ashi was elderly when Rav Achai lived and thus Rav Ashi was responding to the younger Rav Acahai.