There's something else I want to check with child Ikki so I'll get back to you regarding how long and when. Hopefully soon.

Yoh is 15 in canon and I don't think he forget that he's 16 in Luceti since his birthday just passed. He's the older brother!! Yosh!!

Goku won't have much this event, he will be in that aged up state half the event, 5 or 6 days but Natsuno can change back to normal or anything else at any time you want if that's too long for you.