(V): [ Aristotle concludes, "That there never was a time when there was not motion, and never will be a time when there will not be motion" ]

But then he says...

[ Since everything is moved by something and since motion is eternal, Aristotle concludes that there must be something that imparts motion without itself being moved; otherwise, there would be an infinite regress of movers, the moved and instruments of moving, which is unacceptable (Physics 8.5). (An axiom for Aristotle is that an infinite regress is impossible.) ]

How can an infinite regress be impossible if "there never was a time when there was not motion"?

He appears to be talking about an eternal universe in which the unmoved mover is able to overcome the problem of an infinite number of past events. I don't know how, because if "there never was a time when there was not motion" then there never was a starting point, which means there must be an infinite number of past events. His argument is self defeating, unless we are able to factor in how an unmoved mover can be the starting point for something that never started because "there never was a time when there was not motion".