So-called early onset Alzheimers can develop in early middle age. Occasionally onset may be in the 30s, but thankfully it is very rare and accounts for only about 10% of all cases of Alzheimers disease.
People over the age of 65 are most frequently affected at which point the condition is labelled late onset. The incidence of Alzheimers disease increases with age and by the age of 85 years nearly half of all people are affected by it.
More women than men appear to be affected by Alzheimers disease. It has been suggested that this only seems to be the case with late onset cases and the fact that women tend live longer than men.