Why did Shimon and Levi kill the people of Shechem before they killed Shechem, the perpetrator of the sin?
Seforno: Because Shechem and Chamor were hiding, and they were only able to kill them once they found them.
Ohr ha'Chayim: Because the people were protecting their king and they could kill him only after they killed all the other males. 1
Was it necessary to kill even the very old men, but not any of the females? Perhaps some old people are strong (e.g. Yaakov), but can pretend to be weak, so they killed all of them. Or, perhaps it was common for old people to be strong before Yaakov prayed that people get weak before they die (Bava Metzia 87a - PF).
Why does it say single out Chamor and Shechem, and say that they killed them with a sword?
Ha'amek Davar: Shechem and Chamor circumcised days before the rest of the city. 1 When Anshei ha'Ir were in pain on their third day, Shechem and Chamor were healthy, and they needed to kill them in war. This was not needed for the people in pain.
Refer to 34:24:152:1.
