Genèse 37:3

Son of old age...for he was born to him at the time of his old age, but Onkelos translated: "wise son," all that he learned from Shem and Ever he passed to him. Another explanation: his appearance was like his, similar to him.

פסים. expression for garment of fine wool, like“green wool (כַּרְפַּס) and blue” (Esther 1:6), and like the k'tonet passim of Tamar and Amnon (2 Sam. 13:18). But Midrash Agadah references his troubles, that he was sold to Potiphar , to the sochrim, to the Yishmaelim, and to the Midyanim.

And Israel loved Joseph more than all his sons, because the likeness of Joseph resembled his own, and he made him a figured robe.

For he was a son of old age. As it sounds, for he begat him when he was 91. His brother Binyamin they also called "child of old age." And after these two none were born to him.

passim, embroidered tunic. Passim is like pas yada (palm of the hand) in Aramaic.

BECAUSE HE WAS THE SON OF HIS OLD AGE. That is, he was born to him during his old age. Onkelos translated: “he was a wise son to him,” for all that he had learned from Shem and Eber he transmitted to him. Another interpretation is that the facial features of Joseph were similar to those of Jacob. This is Rashi’s language. Rabbi Abraham ibn Ezra also explains it in this way: “Because he was the son of old age — for he begot him in his old age when he was ninety-one years old. They likewise called his brother Benjamin a little child of his old age. “
But in my opinion this is not correct for the verse states that Jacob loved Joseph more than all his children because he was the son of his old age, whereas all his children were born to him during his old age! Issachar and Zebulun were not more than a year or two older than Joseph.
The correct interpretation appears to me to be that it was the custom of the elders to take one of their younger sons to be with them to attend them. He would constantly lean on his arm, never being separated from him, and he would be called ben z’kunav because he attended him in his old age. Now Jacob took Joseph for this purpose, and he was with him constantly. He therefore did not accompany the flock when they went to pasture in distant places. And Onkelos who translated, “he was a wise son,” intended to say that in his father’s eyes, Joseph was a knowledgeable and wise son, and his understanding was as that of elders. However in the case of Benjamin, who is called yeled z’kunim (a little child of his old age), Onkelos translated: bar savtin, as in the case of Joseph. (a son of old age). [The explanation of Onkelos in the case of Joseph becomes clear] because the verse here does not state, “Joseph hayah (was) a son of old age;” instead, it says, hu lo (he was unto him), meaning that in his eyes he appeared to be [a ben z’kunim, and consequently it must mean bar chakim, a wise son]., which means that Joseph was a wise son in his father’s estimate. This is the intent of the Sages when they said: “Whatever Jacob had learned from Shem and Eber he transmitted to him,” meaning that he passed on to him wisdoms and the secrets of the Torah, and that the father found the son to be intelligent and profound in these areas as if he were an elder and a man of many years.

וישראל אהב, all of the aforementioned details caused the brothers to become jealous of Joseph.

בן זקונים, he was the most recently born of 11 children. There had been a considerable interval before Binyamin, the last of Yaakov’s children was born. Yaakov’s inordinate love for Joseph developed long before Binyamin was born.

כתונת פסים, a cloak, (compare Samuel II 13,18 Tamar’s cloak).

ועשה לו כתונת פסים, as a visible sign that Joseph was intended by him to become the leader of all the brothers both at home and in the field. The use of such distinctive clothing to symbolise someone’s elevated stature is found also in Isaiah 22,21 והלבשתיו כתנתך, “I will dress him (Chilkiyah) in your tunic,” where it signals that authority is transferred to the one wearing the appropriate garments. (uniform). The Talmud Baba Kama 11 also confirms that authority is signalled by the attire worn by people possessing it. [there the brothers who had paid extra for their leader to represent them and to appear well dressed are quite content seeing that their representative while attired in costly garments will indirectly confer benefits upon them through their brother being listened to in the councils of the city. Ed.]

כי בן זקונים, what was so special about Joseph’s age, seeing all the eleven brothers had been born in the space of 7 years? How much older was Yaakov at the time Joseph was born than, say, at the time Yehudah was born? We conclude therefore, that the meaning of the word זקונים has nothing to do with physical age, but that Joseph appeared to him as especially intelligent, wise, wise well beyond his years. The words of wisdom spoken by Joseph would normally be expected only from the mouth of men who had acquired such wisdom through having lived for many years. This is also the way Onkelos understood the term when he translates it as בר חכים, “a wise son.” Seeing that he considered him so wise he dressed him in especially attractive garments. In this way he gave tangible expression to his special love for him.

ועשה לו כתונת פסים, the word פס is related to the same word in Daniel 5,5 פס ידא, palm of a hand. The cloth was made of differently coloured surfaces similar to garments made of soft wool which are made in a number of differently coloured stripes or sections. The garment looked very impressive, arousing the hatred of the brothers in addition to the fact that they hated him for spreading tales about them to their father. Our sages in Shabbat 10 seize upon this detail to teach us that a father must ever be careful not to arouse inter-fraternal jealousies, seeing that the fortunes of the Jewish people have been so negatively affected on account of five silver coins worth of angora wool which Yaakov spent more on Joseph’s attire than he did on the garments worn by his other sons. The enslavement of the Jewish people in Egypt was brought about as a direct consequence of this jealousy.

כתונת פסים, “an embroidered garment;” extending down to the palms of his hands.