Yoshida did not make it about the under-18 crowd. He's very clear who he's aiming for: "That's why we don't feel those types of games are a threat because the basic game is designed completely differently. Because the audience that's playing Overwatch and Fortnite are probably in their 20s, they're a younger audience. If that younger audience becomes our main audience for FF14 or our current MMORPG ..."
Did he mention an under-18 crowd? No, he did not.