Maybe that is one reason why modern and traditional payment can't replace each other. Because people itself is different, not only depends on age but not all people maybe can access mobile phone or anything like that so they still can do payment with fiat. I think it is no matter it is digital or traditional payment, but currency still currency. People use it as payment and they can buy something with it no matter who are them.
Correct, if a technology like Bitcoin becomes the new standard and people would have reason to participate in it but can't, that's also kind of exclusive, which Bitcoin is not supposed to be. I don't know though how critical the situation is when it comes to mobile phone distribution. I guess most people have access to mobile phones? I have no idea about those statistics but that might be one of the smaller problems to solve.