I'm glad you asked. Corbulo Academy was destroyed in 2526. John was born in 2511. That makes him 15 at the time. That video that shows the Spartans and Innies fighting together was taken in either 2526 or BEFORE that. Which means they were 15 or younger in that video. Do you see where I'm getting at? Sully isn't the only one alive whose seen that video either.