Well, it is natural for the organs to begin to fail in some aspects as time goes by. I think it first starts with the memory. After a while, people begin to forget the smallest details and you find them asking some questions over and over again. I've seen this firsthand and it just breaks my heart. No one should have to go through this. It doesn't happen to everybody of course just as some people age far slower than others. I've seen fifty years old bent with age and I've also seen a 90+ man who requires no walking aid and doesn't use glasses. It might be genetic, I'm not sure but some people definitely age slower.
I however think that with adequate training, the senses could be taught to last longer. Just as some experience moments of blankness in thoughts, some could also learn to have longer span of memories. I think one of the causes of short lived memories is because people do not take conscious efforts to strengthen their memory retention capabilities and this can also be said for smelling.
The senses weren't made to be rigid. Everything can be bettered with deliberate effort. That is the truth of the matter.
Also, I think with the loss of one sense, another becomes better, or the others. This isn't a given and I can only say so because I've seen an analogy displayed in the movies. What do I know?