According to the same study quitting before the age of 50 shows quicker decreases in lung cancer risk.

They also looked at women but apparently they didn't get enough women smokers in Korea to have statistical power to draw strong conclusions so ymmv. jamanetwork.com/journals/jam....

Cancer Risk Following Smoking Cessation in Korea

This Korean cohort study investigates the time course of cancer risk according to the time elapsed since smoking cessation and the benefits of smoking cessation according to the age at quitting.