At this point, just make the entire site 16 already. Roblox clearly doesn't want to deal with 15 and under players. It's no longer the game it was when I was a kid.
When your game has had fewer than 100 highly engaged players over the last 60 days, users under the age of 16 will no longer be able to play it.
If a game is limited, it can regain access for Kids/Select users once the game has had 500 highly engaged players over the last 60 days.