Musar su Salmi 107:1

The Torah reports Joseph as being 17 years old. This number was not reported without good reason. We have explained how Jacob in his capacity of representing the emanation תפארת, which is the "home" of the four-lettered Ineffable Name embodies that name, and how in particular the letter ו in that four-lettered-Name alludes to Jacob. We have also described Joseph as a miniature dimension of that letter ו, and how Joseph too serves as a kind of מרכבה, for G–d's Name in a "miniature" way. That "miniature" is the mystical dimension of what we call “מספר קטן,” i.e. numerical values arrived at by omission all digits "0." The מספר קטן of the four-lettered Name amounts to 17 (5=ה+;6=ו+;5=ה+;1='י total 17). A way of remembering this is the verse: הודו לה' כי טוב; the numerical value of טוב is 17. This is why the Torah reports Joseph's age when he was 17. The Torah adds that he was still a נער, a boy.