I received this via e-mail from R. Daniel Eidensohn, with permission to post:
This Shabbos (June 17, 2006) I had the opportunity to ask Rav Shmuel Kaminetsky about the issue of the age of the universe. As some of you are aware, the issue is heating up again. There are some who would claim that Rav Shmuel has changed his position on the matter or deny that he ever permitted belief in a greater than 6000 year old universe. I had only a short time to speak to him so I limited myself to this issue.
I asked him, "Is it permitted to believe that the world is more than 6000 years?"
He responded that it was permitted since we don't have a clear understanding of the view of Chazal in this matter. He supported this assertion by citing a number of medrashim e.g., that there were worlds before this that were created and destroyed. Consequently we simply don't know how much time the original process of creation took. I mentioned that there are gedolim who have asserted that since the majority of gedolim reject the view that the world is more than 6000 years old that is is kefira to assert such a position today. He said he was aware of such an assertion but disagreed with it. He noted that in fact the discussion about the age of the universe is not a new topic. He said that Rav Avraham ben HaRambam disagreed with the approach of these gedolim and that after Techiyas HaMeisim these gedolim would have to explain to Rav Avraham ben HaRambam why they disagreed with him.
In sum, I have recently asked two gedolim [Rav Shmuel and R. Yisroel Belsky - GS] about whether it was permitted to believe that the universe is more than 6000 years old and both unequivocally responded that it was permitted. Both based themselves on
the fact that we don't have an unambiguous mesora regarding the meaning of relevant statements of chazal and rishonim. Both of them also acknowledged that the majority of gedolim today disagree with them.