The charm of knowledge would be small, were it not that so much shame had to be overcome on the way to it. - Friedrich Nietzsche
So it turns out that it is indeed mathematically possible for Moulay Ismael to have fathered 888 children, which makes the Biblical accounts of Rehoboam's 88 children sounds not so implausible, of for that matter, Gideon's 71 and Ahab's 70.
But what about old age? In the Old Testament, it is claimed that Adam, the first human being, lived for 930 years - nearly a millennium, which is a little hard to accept. But according to the Book of Genesis, Seth, Adam’s third son, lived for 912 years. A person named Jared is said to have lived 962 years, and Noah was 950 when he died. The record holder is Methuselah, who lived to be 969 years old.
Although not nearly as unbelievable as the Old Testament accounts, there are some pretty hard-to-accept claims in the Chinese traditions. Zen Masters are said to have lived exceptionally long lives, and Bodhidharma, the First Chinese Patriarch, reportedly lived to be 150 years old, while Joshu lived to be 120. These might be exaggerations, but Zen Masters do tend to live long (vegetarian diet, low stress, and they usually don't drive in cars), and if you want a modern, if scandalous, example of the longevity of Zen Masters, Joshu Sasaki died just last year at 107, but in 2013 was still sufficiently active that he was accused of groping and sexually harassing female students at the age of 105.
The Buddhist tradition has some pretty unusual claims at the other end of life as well. The Buddha is said to have named his son Rahula, which by some traditions means "fetter," as the Buddha realized that with the birth of a son, he would be forever shackled to family life (Father of the Year material, that Buddha). But in other traditions, Rahula is translated as "obstacle" because it is claimed that he remained in his mother's womb for six years before he was born.
And this is not even the most extraordinary case of late birth. There was Lao Dan, who is said to have stayed in his mother's womb for eighty-one years (patient mother, there). Then there was the famous case in China of Lao Lai Zi, who had white hair and eyebrows when he was born and could talk from the moment of birth. He was born old, but nevertheless, he still acted like a child and was very rambunctious.
Modern research would probably reveal that these supposed late births were actually cases of progeria, popularly known as the "Benjamin Button disease," combined with the lack of accurate record keeping and birth certificates at the time. If it appears that a child had been born "old," rumors would have it that he must have grown old in the womb, and with time those rumors became legends, the legends became accepted as fact, and when they got recorded in the anthologies and koan collections, the "facts" became scripture. If an ancient Zen Master looked 150 years old, and there was no documentation to disprove it, then everyone soon accepted that he was 150 years old. It's not a case of miracles or divine intervention, and a little science and knowledge shed on the matter might reveal some interesting things.