Or Uncertainty of Ages, depending on how you prefer to look at it.
* Darius I the Great was crowned at age 30 in the year 522 and died in 486. (36 years)
* Xerxes I reigned from 486 to 465. (21 years)
* Artaxerxes I reigned from 465 to 425. (40 years)
Let's tabulate this:
Darius : 522 - 486, 36 @ 30
Xerxes : 486 - 465, 21 @ ?
Achaemenes : 486 - 460/1, 26 @ ? (satrap)
Artaxerxes : 465 - 425, 40 @ ?
OK, let's start the Maths:
Darius was 30 when raised to King of Kings, and lived 36 years more => 66 years old. Xerxes and Achaemenes were both sons of Darius. Xerxes was the oldest son and had been designated heir as far as in 498, therefore we know that, at least, he lived 33 years, plus the age he had by then (he was prince-heir, ruler of Babylon as King's governor).
He must have been 16 years old, I'd say 18, but anyway, at least he lived 33+16=49 years.
Achaemenes was born before 486. Actually he was born before 495, because he was the stratégos commanding the fleet at Salamis in 480, and he must have been at least 15 years old, probably more. He was, at least, 15+30=45 years old when he died, probably at least 50 if we take he was about 20 at the Battle of Salamis (and Thermopilai! the year before the Battle of Plataea). Probably more, he may have been already born when Darius was made King, for all that we know.
When Ahmoseh/Amasis died in 526 he was pretty old, after ruling for a lot of years, since 570 (when he was already an adult). Around 65 years old, I'd say. His son, Psammetichus, ruled for a single year, killed by Kambyses in 525. He was young when he was crowned Pharaoh, and already had son(s) and wife(s). Lets put it about 25 years old (a pretty, round number).
Inaros was Psammeticus III's son. He died circa 454. Therefore, he was, at least 524-454=70 years old (in the event he was born after his father's death). Therefore he was, at least, 64 years old when he started the rebellion and, supposedly, killed Achaemenes.
He was pretty old for a rebel, don't you think? I mean, okay, not that a big deal. But a bit too old to lead an impetuous through the Delta of the Nile he does seem to me.
Now, before doing calculations, yesterday and today, I was toying with an Inaros of about 40-50 years old, in his prime. 60 is a bit past his prime, maybe he was forced to wait for the death of Darius to reach Mareia before daring to rebel against Achamenes.
Another possibility is that he was not Psammetichus's son, but simply claimed to be so, to give some credibility to his claims to the throne as king of the Lybians, and even Pharaoh (mentioned by scholars a Psammetichus IV, otherwise unknown; others equate him to Ramses XI. Considering the number of names Pharaohs had, it could very well be, I dunno).
This is pretty important, as my take on the character will have to be changed if I believe his claims as they were transmitted to us by Greek historians like Thukidides. We do know that the new satrap of Egypt gave important adminitration posts to both Inaros's and Amyrteus's sons. If this force me to change Amyrteus's age as well (and make him older than the 20-30's I'm guessing) I'll hang myself from the foremast by the thumbs for a while... :-P
Anyway, History is interesting, uh?
Oh, the book! I've updated my work in progress counter with almost 3,000 more words. However I'm writing slower now, because Men of Bronze is sucking my writing time on the train and cafés... OTOH, I'm having such a great time... :-)
I'll get the Greeks to Egypt in time to play their part, worry not ;-)