Let's say that Alexander wasn't born in 356 BC, but two hundred years later in a hellenistic empire in Anatolia. So, he would've been born in 156 BC in the Kingdom of Pontus. During 200-100 BC the Romans were quite busy with fighting their way to the east, and they also fought in Anatolia.
Alexander, becoming king at the age of 20, reorganises the army, reintroducing the once mighty phalanx and the cavalry. In 125 BC he's ready to fight the Romans, with his trained army, a good amount of money and his own leadership. Would Alexander beat the hell out of the Roman legions? Would it become a long struggle? Would Alexander end up like Pyrrhus, leaving the Romans alone after some years? Would Alexander take... Rome?