Daiya used to lie about his age when he was in middle school to be able to get a job (actually he had three of them) to earn money to feed his little brother, since the money their father sends usually goes to taking care of their mother and pay whatever bills it can cover for the most part. He was always a very tall kid and had no problem acting more mature than what you’d expect for his age, so he fooled people easily.
Have a cute one to balance that out: Mondo was a late walker because when they were little, Daiya used to carry Mondo around everywhere, to the point where baby Mondo just had to point to where he wanted to go and Daiya would take him. After a while, little Daiya sat his little brother down and tried to explain to him how it was time to leave childish things behind and learn to walk. Baby Mondo just toppled over and started trying to put his toes in his mouth and still won the argument.