Yah another episode!!! In China, the legal marriage age is 20 for girls and 22 for boys. You are right, Sang Zhi is 19 right now, so Jiaxu said to give it 2 more years 😏 which we all know it's gonna happen eventually.
So what I'm getting from this is that the legal marriage age works like the legal drinking age, right? It's saying you're an adult legally at 18 but not old enough to marry/drink yet.