Can long-term usage of aluminum kettles cause Altzheimer's or another disease, considering the fact that the water inside is heated to 100 C?
We don't know how risky aluminum is. (Source.)
In Germany, the Federal Institute for Risk Assessment (BfR) wondered about kettles too.
They wrote an article named "FAQs about aluminium in food and products intended for consumers". I shall quote a bunch from that article; their final answer to your question is at the very end of my post.
What health risks does aluminium absorption pose?
Any assessment of the hazardous potential of aluminium focuses on its effects on the nervous system and the fact that it is toxic to reproduction (effects on fertility and unborn life) as well as the effects of aluminium on bone development.
When aluminium is ingested with food, its acute toxicity is low. ... But even in healthy individuals, the light metal accumulates in the body in the course of a lifetime, especially in the lungs and the skeletal system.
What quantities of aluminium can be absorbed ... without any health risks?
For oral intake from food, the European Food Safety Authority (EFSA) has derived a tolerable weekly intake (TWI) of 1 milligramme (mg) of aluminium per kilogramme of bodyweight.
Finally, later in their article, they answer your question:
Can I continue to use aluminium cooking pots / pressure cookers?
Provided that they are coated, yes. If they are not, no salty or acidic foods such as apple purée, rhubarb or salted herring should be prepared or stored in such pots.
So it sounds like they say you can continue to use your aluminum kettle.
The Aluminum-Alzheimer's connection is very controversial - esp in regard to vaccine adjuvants.
Nevertheless, here is an excellent video describing the underlying concerns
The upshot is, including silica rich mineral water in the diet can help excrete aluminum that has accumulated in the body.
To address your question: might want to exchange the aluminum pot for a steel one.