I think it has been the best way to save and hodl the value of their money through lifetime. Also, it is a traditional habit as well. For example, my grandparents use all their saving money buy Gold and when they passed away, they splited their gold into different parts and gave those to their children.
It was good but in past when bitcoin and other crypto currencies were not introduced, but now I think that bitcoin investment is too much good and profitable than gold and silver, in fact we can see a very slight change in bitcoin price after years, while investment in bitcoin or other crypto currencies can give a good profit I few days.
Not only old people but all those who arent much exposed to this new technological world. You are required to give them solid reasons and evidences that can compel them to believe in bitcoin. Things arent that much easy when it comes the case of old people. They are already distant from the modern technology so this virtual thing is a blast for them. It is really hard for them to believe this imaginary thing.