A moments thought shows there can be no centre of an infinite expanse of space, it has no geometrical sense. When Aristotle places the Earth at the centre, he can surely only mean that its the meaningful centre, the place where anything of any importance can take place. Is this right?
Why did Aristotle place the earth at the centre of an infinite universe?
He placed the earth at the center of a finite universe. For Aristotle, the universe is decidedly not infinite; he argued that there were potential infinities, but not actual infinities.
Aristotle didn't put the world at the center of the universe per se. Rather, he deduced it from his system of metaphysics and common sense observations of reality.
The world is comprised mostly of the element earth. Earth, being the heaviest of the four classical elements, tends to fall towards the center of the universe (it's natural place) if it is displaced from there. Since the world as a whole including the earthy surface beneath our feet isn't currently falling out from under us, it must already be at rest at the center of universe.
(How people were satisfied with teleological arguments for 2000 years, I'll never understand.)