For a restaurant serving what was until recently a Class 5 narcotic substance, the clientele appeared older than one might expect: a couple of extended families, including grandma and grandpa; a woman having a quiet lunch with a man who appeared to be her father; a low-key middle-aged couple. Even the decor—cheesy knick knacks, thick curtains, antimacassars, antique crockery—was far from edgy. The setting was Ban Lao Reung, a restaurant in Prachinburi, Thailand, that recently became the country’s first to serve dishes made with cannabis. On the day I visited,…