That is still hypothetical. I can't know how he would have experienced it at age 12, but Charles was always mature, regardless of his age. He was not a scatterbrain. He was just a normal teenager. He was very calm and very collected. In his case, he probably would have been just as mature at the age of 12 or 13.
As I said, the sick children I have seen, both toddlers and older kids, were calm about being sick. I talk a lot with other parents who have also lost their child, and it was their child who helped them. It is our children who help us get through the illness and then get through the grief, because they themselves accept it, quite simply. They have the maturity, the resilience, that enables them to accept the illness, to live with the illness, to do what has to be done to overcome it or to accept death when they can't overcome the illness.
Would Charles have made the same decision? Would he have been at the end of his rope at age 12, too? Probably yes, but we will never know. The fact remains that the situation would have been the same and there would have been the disease and all the same problems for two years.