https://www.tandfonline.com/doi/full/10.1080/13102818.2020.1820378 RF radiation could be a cause, it is completely unmonitored.

Drug and alcohol abuse, probably. https://americanaddictioncenters.org/alcoholism-treatment/brain-damage

Being taught to live a bad lifestyle. Dementia isn't the only "old age" issue younger people are experiencing. High blood pressure, diabetes, COPD, and other problems are being seen as well. The reason is chronic dehydration. Older people's nutritional requirements are the same as anyone else, yet, they develop problems that are most commonly associated with old age. It's not the age, but the lack of water. Water regulates every function in the body. When you don't stay properly hydrated, cells and the various organs will develop problems, giving you signals of their need for water - such as high blood pressure, high cholesterol, asthma, &c. The pharmaceutical industry labels these symptoms "disease" and prescribes their medications that only treat the symptoms but do nothing for the condition. This is how they make their huge profits. Based on the laws of physics, if you eliminate the cause of a disease that disease has no reason to exist. Thus, the medical profession writes prescriptions that only hide the symptoms until the medications wear off - then the symptoms return, requiring more medications. As a person ages, his perception of thirst gradually diminishes until, by the time they reach an advanced age, it's almost non-existent. In the case of younger people, they have soft drinks and other water substitutes too freely available to them so that they don't drink enough water. Thus, they develop the same issues as the elderly. Soft drinks and other substitutes are not the same as water - they have a diuretic effect that forces water out of the body. There have also been studies that indicate common table salt contains an aluminum substance that is speculated to cause Alzheimer's disease. Salt is not bad for you as doctors claim, but it needs to be unprocessed sea salt, not the bleached garbage commonly purchased in grocery stores. That salt is so deficient in nutrients that iodine has to be added back in.

some reflux tablet's and cholesterol meds cause it also

I have a friend that is 64 and has it.

In a technological world, digital dementia is the cause. Young people increasingly rely on technology instead of their brain.