I think it will sure be difficult for them, but i guess if bitcoin is really adopted massively and being used as daily currency, people will think how it can be modified to suit blind people. Like for example, before blind people have it difficult, but there will always be innovation made so it will be easier for them, that's the same with bitcoin i guess, many bitcoin users might think what to do to help them, maybe programming some app to help them, make a voice-based app so it'll be easier for them to use since they can't see and others. While for eldery people, it might be hard to teach them, since most of them don't want to learn anymore. However we can slowly teach them, giving tutorials, simple explanation and such, if they really want to, they will be able to. People around them should be willing to help as well.