According to John Sorenson, when we consider the interrelations between Ishmael's and Lehi's families, the age distribution of Ishmael's offspring probably was about like this:
Child Age on Leaving Jerusalem
Daughter 1 (married Zoram) 31
Son 1 29
Son 2 26
Daughter 2 (married Laman) 24
Daughter 3 (married Lemuel) 21
Daughter 4 (married Sam) 19
Daughter 5 (married Nephi) 16
(The order and ages of Daughter 1 and Son 1 might be reversed.)
[John L. Sorenson, "The Composition of Lehi's Family" in By Study and Also by Faith, Vol. 2, F.A.R.M.S., p. 187] [See the commentary on 1 Nephi 17:1]
“I Nephi and Also My Brethren Took of the Daughters of Ishmael to Wife”
The Hiltons suggest that if Ishmael and Lehi were related (see Erastus Snow statement in commentary on 1 Nephi 7:1), all the marriages between the sons of Lehi and the daughters of Ishmael (see 1 Nephi 16:7) would be condemned under our modern laws and statutes, but not under the law of Moses.
Perhaps the best known consanguineous marriages were those of Abraham, Isaac and Jacob (see illustration). In one non-biblical account Abraham married Sarai, his brother's daughter (Jasher 12:44). The Bible says she was Abraham's half-sister (Genesis 20:12). Isaac married Rebecca, his double first cousin once removed (his mother's sister's granddaughter and his father's brother's granddaughter). Jacob married Rachael and Leah, his first cousins (his mother's brother's daughters).
Among desert tribes of today, cousin marriages are a common practice. . . . Additionally in ancient times and continuing to the present in the Middle East, marriages were not love marriages but were arranged by the parents. Indeed, in many cases the bride and groom met for the first time on their wedding day. . . . This pattern may appear strange to the liberal western mind. . . . More especially it would have been strange to the mind of Joseph Smith. [Lynn M. and Hope A. Hilton, Discovering Lehi, pp. 69-74]
1 Nephi 16:7 I Nephi . . . and also, my brethren took of the daughters of Ishmael to wife ([Illustration]): Near Kin-Marriages of Abraham, Isaac and Jacob. [Lynn M. Hilton and Hope A. Hilton, Discovering Lehi, p. 71]