However we read in Josephus, The Jewish War (William Whiston Translation, 1737), VII, 9, 1. Online.
“Yet was there an ancient woman, and another who was of kin to Eleazar, and superior to most women in prudence and learning, with five children: who had concealed themselves in caverns under ground; and had carried water thither for their drink; and were hidden there when the rest were intent upon the slaughter of one another.
Those others were nine hundred and sixty in number: the women, and children being withal included in that computation.”
John Allegro (The Chosen People: A Study of Jewish History from the Time of the Exile Until the Revolt of Bar Kocheba. Hodder and Stoughton, 1971: 240-1) comments:
“It might be considered ungracious to speculate on the identity, or even true sex of the ‘old woman’. described as ‘a relative of Eleazar’s’. and as being ‘superior in prudence and training (phronesi kai paideia) to most women’, who hid her female companion and accompanying five children underground during or after the mass slaughter of their fellow-Zealots above. Perhaps, too, we should not enquire too closely how that prudent person could so ‘lucidly report both the speech (of Eleazar) and how the deed was done’, if she were in hiding the whole time.
Nevertheless, one cannot help wondering if Josephus did not come by his remarkably complete knowledge of these last dramatic days and hours of Masada’s resistance through the first-hand report of Eleazar himself. Does Josephus know more about the ‘relative of Eleazar’ and her ‘prudence’ than he cares to divulge? Certainly, if Eleazar had felt no guilt in escaping the suicide pact disguised as an old woman, and was thus enabled to usher perhaps his wife and family from this tomb of Zealot hopes, he would have had some sympathy from Josephus, who had done much the same thing earlier on in the war.”
Certainly an interesting hypothesis. Almost all other writers neither repeat this hypothesis, nor refute it. It is of course a problem that the only evidence either way is the account by Josephus.
Eleazar would of course have worn a beard, and to pass as an old woman would need to have shaved. Shaving technology at this period was rather primitive - it was probably done simply with a sharp knife, and would leave cuts on his face. However the Romans might have respected an old woman enough not to have removed her veil.