HONG KONG (AP) — Born after the historic July 1 day when Britain handed Hong Kong back to China in 1997, the 18-year-old protester who was shot at close range in the chest by a police officer during violent demonstrations this week and then arrested in the hospital is part of a generation for whom the clock is ticking.

In the lifetimes of young Hong Kong citizens born after 1997, the sands will run out on China’s promise _ enshrined in the territory’s constitution _ that Hong Kong’s “capitalist system and way of life shall remain unchanged for 50 years.”

That looming deadline and uncertainty a...