Joseph: What Kind of Son Was He in Genesis 37:3?

Genesis 37:3 (ESV) reads:
Now Israel loved Joseph more than any other of his sons, because he was the son of his old age.

Problem: Too Narrow
The main problem I have with this translation is that it narrows the interpretation further than the original does and biases the reader into interpreting this passage to this: the reason Israel treasured Joseph so was that Joseph was born to Israel when Israel was old. Indeed, that is a possible interpretation. But if it is correct, why would not Benjamin (who was surely born by chapter 37) be privileged instead of Joseph?  Benjamin was an even younger son of Israel's. And upon Benjamin's advent, Israel's beloved wife Rachel died, so one would think Benjamin would have enjoyed pride of place.

Translate to Allow the Alternative Plausible Interpretations
The original reads and stands as a good translation by itself: 'because he [was] the son of old age,' that is, the word 'his' is absent in the original mss. The ESV Study Bible makes some helpful interpretation suggestions in a brief note. I lean towards their second option, as Israel seemed to keep Joseph close by to him, sent him on special missions, and mourned unconsolably upon Joseph's 'death'.  ESV, page 114:

the unusual Hebrew expression 'son of old age' (there is no explicit word for 'his' in the Hebrew text) may denote [1] someone who displays exceptional maturity while still young or [2] perhaps the son closest to Jacob in his old age. Jacob may have recognized Joseph's leadership potential early in life.