C. F. Keil and Franz Delitzsch on Ecclesiastes 11:10

Ecc 11:10 “And remove sorrow from thy heart, and banish evil from thy flesh: for youth and age, not yet grown to grey hairs, are vain.” Jerome translates: aufer iram a corde tuo, and remarks in his Comm.: in ira omnes perturbationes animi comprehendit; but כּעס (R. כס, contundere, confringere) does not signify anger, but includes both anger and sorrow, and thus corresponds to the specific ideas, “sadness, moroseness, fretfulness.” The clause following, Jerome translates:et amove malitiam a carne tua, with the remark: in carnis malitia universas significat corporis voluptates; but רעה is not taken in an ethical, but in a physical sense: כעס is that which brings sorrow to the heart; and רעה, that which brings evil to the flesh (בשׂר, opp. לב, Ecc 2:3; Pro 14:30). More correctly than the Vulgate, Luther renders: “banish sorrow from thy heart, and put evil from thy body.” He ought to free himself from that which is injurious to the inner and the outer man, and hurtfully affects it; for youth, destined for and disposed to joy, is hevel, i.e., transitory, and only too soon passes away. Almost all modern interpreters (excepting the Jewish), in view of Psa 110:3, gives to שׁחרוּת the meaning of “the dawn of the morning;” but the connection with ילדוּת would then be tautological; the Mishn.-Midrash usus loq., in conformity with which the Targ. translates, “days of black hair,” proves that the word does not go back to שׁחר, morning dawn, morning-red, but immediately to שׁחור, black, and as the contrast of שׂיבה (non-bibl. שׂיבוּת, סיב, סב), canities, denotes the time of black hair, and thus, in the compass of its conception, goes beyond ילדות, since it comprehends both the period of youth and of manhood, and thus the whole period during which the strength of life remains unbroken.The Mishna, Nedarim iii. 8, jurist. determines that שׁחורי הראשׁ denotes men, with the exclusion of women (whose hair is covered) and children. It is disputed (vid., Baer’s Abodath Jisrael, p. 279) whether תּשׁחרת, Aboth iii. 16, Derech erez c. II., Midrash under Lam 2:11, is = שׁחרוּת, but without right; ben-tishhorěth is used for a grown-up son in full manly strength.