Radak: In Yerushalayim, and in the rest of Eretz Yisrael. Yerushalayim is primary; it is the head of Malchus Yisrael. It says "mi'Sham", for a Mes will not go out from there to burial.

Rashi: It is a youth, like "Olel" (Eichah 2:11). Radak - Ziknah is at 60 (Avos 5:21), and he did not complete his days until 70 ¹ . That is in this world. Then, they will not say that a Zaken complete his days until he is 300 or 500. This is like the first generations, at the time of creation of the world, such long lifetimes applied to the Klal, or to individuals. In the future, it will be for the Klal of Yisrael.

Rashi citing Bereishis Rabah: At 100, he will be liable for punishment, to be Chayav Misah for a capital Aveirah.

Radak: If one dies at the age of 100, this will be due to his sin. They will say that he died as a youth.

Malbim: The verse explains why crying will not be heard. Nowadays people cry over one who died before his time. Then will not be found a youth or elder who did not complete his days. Nowadays it is found, when his basic moisture and natural strength cease. This is called Zaken. Nowadays, he weakens at 50, it is premature. Man's nature is to live 900 years, like we find in the first generations! People die as youths due to illness or sin. Also this is premature. In the future, even for sin one will not die before 100. This will be the age for punishment bi'Ydei Shamayim.

Rashi: This is for an Aveirah that mandates excommunication.

Radak: This explains "ha'Na'ar Ben Me'ah Shanah Yamus"; this will be Hashem's curse. He is a sinner when he dies at 100.