I honestly can't tell you- you'd need a situation analogous to Rome, wherein Athens defeats the other cities early and decisively while also avoiding Persian suzerainty. Rome was lucky in that aspect- it conquered the other cities and managed to defeat its various enemies over the course of centuries, thankfully far away from the Persians and later the Diadochi. Brennus is nowhere near as frightening as the full might of Iran and Aniran.
Athens is neither- it is telling that it was a simple monarchy, rather than a Republic, that ended up conquering the East. Athens would, in its period of ascendance, not only fend off various Sparta-and-the-Fuck-Athens-Society attacks but also client-state dissent and the Achaemenids at the height of their power. Rome never faced a power as theoretically superior to it as the Achaemenids- Carthage and Epirus were equals, whereas Athens was theoretically miniscule next to Persia.
Internally, the system of government was less sophisticated than that of Republican Rome; the finer workings of a Senate and the class system had not yet been worked out. You'd also need a more directed foreign policy, rather than, for example, having Alcibiades kip off to Sicily whilst fighting the Spartan coalition. You'd also need to retain people like Themistocles, who, like Alcibiades, eventually alienated enough of Athens' fractious society to flee and become a very effective satrap in Asia Minor.
Perhaps if you crippled Sparta with a Helot revolt at the right time- and got the Achaemenids to go attack Nubia or India or something- Athens could manage to suborn enough cities to establish a true hegemony over most of Hellas. This would leave the fringe kingdoms- and Sicily- largely out of grasp. It would then need to win something like the Social Wars against these cities- it would need not only a big navy but also an effective land force for those cities inaccessible by land.
And this is forgetting x-factors like plague, which damn near ripped apart Athenian society down to the roots OTL.