How can one reconcile religious estimates indicating that the age of humanity ranges between 6,000 and 10,000 years with geological and fossil evidence pointing to human remains dating back hundreds of thousands or millions of years, in addition to the estimate that Noah's Ark is approximately 90,000 years old? Is it possible that Adam lived millions of years ago?

There is no explicit text in revelation that specifies the age of humanity. One must not confuse the immutable texts of revelation, which are to be believed, with the interpretations and elaborations of some, and with the texts of the Isra'iliyyat (Judeo-Christian traditions) upon which no belief is built. Since knowing the age of humanity does not result in any religious or worldly benefit, a Muslim should not preoccupy themselves with it. Rather, they should occupy themselves with what benefits them in matters of their religion and their worldly life.