俱舍論疏 12.148

12.148

論「此三災起至人壽漸增」，此述三災住時分也。刀兵最速，飢饉最長時。皆言七者，三災起時法爾如此。

The treatise says: "When these three disasters arise … human lifespan gradually increases." This relates the duration of the three disasters. Weapons are the fastest, and famine lasts the longest time. They all state "seven" because it is simply the nature of things when the three disasters arise.