I think if he has late onset (and probably does if he was undiagnosed until 5) he won’t die but he will have all the problems stated above - shortness and early puberty.  I think someone told me that boys with late onset only need their medication until they stop growing and then may need to take it if they have problems with infertility or losing their hair.  Maybe your relatives will be more receptive if they know it’s only temporary.