The day Isaac was weaned, Abraham prepared a big feast. Apparently on that occasion Sarah noticed Ishmael “poking fun” at his younger half brother Isaac. (Ge 21:8, 9) Some translations (JB, Mo, RS) say that Ishmael was only “playing” with Isaac, that is, in the sense of child’s play. However, the Hebrew word tsa·chaqʹ can also have an offensive connotation. Thus, when this same word occurs in other texts (Ge 19:14; 39:14, 17), these translations render it “jesting” or “joking” and “insult.”

Certain Targums, as well as the Syriac Peshitta, at Genesis 21:9, give Ishmael’s remarks the sense of “deriding.” Concerning tsa·chaqʹ, Cook’s Commentary says: “It probably means in this passage, as it has generally been understood, ‘mocking laughter.’ As Abraham had laughed for joy concerning Isaac, and Sarah had laughed incredulously, so now Ishmael laughed in derision, and probably in a persecuting and tyrannical spirit.” Deciding the matter, the inspired apostle Paul clearly shows that Ishmael’s treatment of Isaac was affliction, persecution, not childlike play. (Ga 4:29) Certain commentators, in view of Sarah’s insistence, in the next verse (Ge 21:10), that “the son of this slave girl is not going to be an heir with my son, with Isaac,” suggest that Ishmael (14 years Isaac’s senior) perhaps quarreled and taunted Isaac with regard to heirship.

Jehovah had told Abraham that as alien residents his seed would be afflicted for 400 years, which affliction ended with Israel’s deliverance out of Egypt in 1513 B.C.E. (Ge 15:13; Ac 7:6) Four hundred years prior thereto would mark 1913 B.C.E. as the beginning of that affliction. Consequently, this also fixes 1913 as the year Isaac was weaned, since timewise the two events, his being weaned and his being mistreated by Ishmael, are closely associated in the account. This means that Isaac was about five years old when weaned, having been born in 1918 B.C.E.

Today, when so many women in the Western world refuse to nurse their babies, or nurse them for only six to nine months, a five-year period may seem inconceivably long. But Dr. D. B. Jelliffe reports that in many parts of the world children are not weaned until they are one and a half to two years old, and in Arabia it is customary for a mother to nurse her young anywhere from 13 to 32 months. Medically speaking, nursing, or lactation, may normally be continued until the next pregnancy is some few months advanced.​—Infant Nutrition in the Subtropics and Tropics, Geneva, 1968, p. 38.

In the Middle Ages in Europe the average age for weaning was two years, and in the time of the Maccabees (first and second century B.C.E.) women nursed their sons for three years. (2 Maccabees 7:27) Four thousand years ago when people lived an unrushed life, and there was not the present-day pressure or necessity to telescope so much into the shortened life span, it is easy to understand why Sarah could have nursed Isaac for five years. Besides, he was Sarah’s only child after many years of barrenness.