When did shaolin monks start using twin hooks?
I’m going to assume you mean hook swords (or tiger hook swords) and not just “hooks.” Reliable information on hook swords is difficult to come by. While sometimes called an ancient weapon and described as dating from the Song dynasty (960-1279) or even earlier, most antique examples and artistic depictions are from the late Qing era (1644–1912) or later, suggesting that they are actually a comparatively recent design. They were also an exclusively civilian weapon, appearing in none of the official listings of Chinese armaments. Surviving sharpened examples point to actual use as weapons, but their rarity, and the training necessary to use them, strongly suggest that they were only rarely used as such.