It is not understood why, however, some people begin to suffer from early-onset Alzheimer's long before reaching retirement age, according to the Massillon Independent in "Alzheimer's not limited to elderly."
Because it is possible for you to get the disease and it could happen much sooner than you think, you need to prepare for it. You need to do something now that you will have difficulty doing after you get the disease.
You need to plan for your estate.
That does not just mean you should plan for who gets your possessions, which you should do. It also means than you should plan for who will help you when you can no longer handle things on your own.
You need a general durable power of attorney, so someone can handle your finances.
You also need a health care proxy, so someone can make medical decisions when you are unable to do so.
An estate planning attorney can advise you on the need and use of these documents.
Reference: Massillon Independent (August 22, 2017) "Alzheimer's not limited to elderly."