<snip>
Old people can use bitcoin just like how we use it. Unless they do not know how to operate a device, then they aren't capable of doing it. Because of that, they will be needing help from other people who are knowledgeable with it... Could be anyone (their son, grandchildren, neighbor, etc.) whom they trust. But if there's no one to help them, then they won't be able to use it.
Everything can be learned if taught thoroughly but if those people doesn't want to learn about it then we can't do anything about it. But that's not the case if more people will have to adopt Bitcoin then those people will be the older people in the future that knew about cryptocurrency/Bitcoin.
To OP, older people doesn't use much fiat or crypto currency in the future when all they will be doing is living their lives to the fullest. It's not a problem if they don't adopt to Bitcoin we'll have more new generation coming to learn and adopt Bitcoin in the future.