This disease affects people from the age of 60 and older mainly but there is young onset Alzheimer's which is where you get Alzheimer's before you are sixty but this is very rare.
Also this disease doesn't actually affect a specific ethnic group but is very common in America.
There is no one for sure cause but scientist say that one of the primary cause is brain infarcts but there is also another way to contract Alzheimer's is there's a 1% chance that you can inherit this disease and this all depends on the number 21 one chromosome.