Malbim: People must honor elders, for [many] days tested them, and they did much good, and they complete their purpose.

Rashi: Tzedakah lengthens one's days.

R. Yonah: It comes to discuss the attribute of Tzedakah. It begins with the praise of old age - it is among the honored crowns, for this is when man's Da'as is complete ¹ . Also, he became wise via his experiences, and understands his end. Since he can yearn for this crown, this will encourage him to desire [giving] Tzedakah, for old age is found in the way of Tzedakah. It says "Mi ha'Ish he'Chafetz Chaim;