Can he not distinguish between good and evil?!
Rashi: I cannot distinguish good food from bad. 1
Malbim: If you want to benefit from my counsel, I cannot give good counsel.
Shabbos 152a: Even though Rebbi had a 93 year old Shifchah who would taste the food, Barzilai avidly pursued relations. This causes old age to come prematurely.
A man may not hear Saros (female singers). This is Kol Ishah!
Rashi (Koheles 2:8): "Sarim v'Saros" are instruments. (Perhaps the same applies here. - PF)
Hagahos Maimoniyos (Hilchos Keri'as Shma 3:16): We are not concerned for a voice that he is used to. Chomas Anach (Koheles 2:8) - perhaps the Saros who sang for Shlomo were his wives 1 and Pilagshim. (We can say similarly for Barzilai. - PF)
Vilna Gaon (OC 75:3): Some Rishonim, including Talmidei R. Yonah, Hagahos Maimoniyos and Mordechai, forbid Kol Ishah only at the time of Keri'as Shma.
Seridei Esh {2:8): One may hear men and women singing together. Chasan Sofer (OC Taharas Yadayim 14) was unsure about this. Tzitz Eliezer (14:7) - this is a minority opinion; most reject it.
Avnei Yashfe 2 (OC 5) #2: The Isur of Kol Ishah is mid'Rabanan. (Perhaps it had not yet been enacted.)
Michlol Yofi (on Koheles 2:8): The Saros were boys with high pitched voices.
Melachim I, 11:3: He had "Nashim Saros Sheva Me'os u'Filagshim Shelosh Me'os."
