So in May, when they opened Bliss Caribbean Restaurant in St. Louis County, Mo., the couple decided to give their customers the same joy — by requiring that all female customers be at least 30 years old, and all men 35.

“We decided to come up with a whole restaurant where adults could pretty much go on vacation for a fraction of the cost,” Mr. Pate said.

This rule has drawn widespread attention to Bliss through social media, resulting in packed dance parties and what the restaurant calls a “grown and sexy” vibe.

But the requirement has also raised some legal questions, as experts point out that the restaurant is treating men and women differently.