The aging (or lack thereof) of superheroes is problematic to address, as most characters are 'timeless' and have remained the same age (essentially) since their creation. Superman and Batman, for example, have been alive since the 30s or 40s, and have never aged beyond their mid-20s-30s (in the main continuity).
The only way to know for sure is to look at time travel stories and use logic (or at least the comic book version of it). Sadly, I'm not familiar with any stories set in the future which feature a 'future' Diana. There are certainly ones that feature future Batman/Superman, as well as other characters, but I've never seen a future version of WW.
Thus, we must use logic. Diana was created by the Greek Gods, and imbued with their powers. Despite being made of clay, she reacts similarly to her flesh-based brethren. Similarly, man was first formed of clay in the Greek Mythologies, so we can assume Diana gains no special abilities from her clay-based body - it has been transmuted into flesh and blood.
She was imbued with powers by six deities, and possesses powers and abilities gifted to her by them. Demeter's gift to her was the strength of the Earth, which provides her with physical strength and durability. Enormous toughness is often seen in other heroes (even non-powered ones such as Wild Cat) to extend your lifespan. Her origin may also grant her demigod status - she's certainly as powerful as some of the lesser gods in DC's pantheons.
Everything thusfar points towards Wonder Woman aging slowly, with an enormously extended lifespan - She is likely a demigod, which would grant her at least some form of enhanced lifespan, if not true immortality, and characters with similar powers have shown tendencies to live much longer than normal.
The final nail in the coffin, so to speak, comes from the Wikipedia article on Wonder Woman:
Diana possesses the ability to relieve her body of physical injury and
toxins by becoming one with the Earth's soil and then reforming her
body whole again. During John Byrne's run, it was stated that this
is a ritual so sacred that it is used only in the most dire of
It does not say this is the case, but a writer could easily take this to mean it restored her body to the way it was when she was first created. This would grant her a form of immortality similar to that possessed by Batman villain Ras Al Ghul - She can be killed, but unless she is she will likely live forever.