Final answer:
The majority of Alzheimer's disease cases occur during old age, typically after the age of 65, with the more common late-onset form. Early onset Alzheimer's is much less common and can start between ages 30 and 60. Genetics are a key factor in the disease's development.
Step-by-step explanation:
The onset age for the majority of Alzheimer's disease cases is during old age, with the late-onset form of the disease commonly beginning after the age of 65. This is the period when most people have retired, and due to aging, may experience various physical declines and increased risks of illnesses such as cancer, and cognitive impairments.
In contrast, early onset Alzheimer's disease, which is associated with genetic mutations in one of three known genes, is much rarer, affecting fewer than five percent of patients and usually begins between the ages of 30 and 60. Genetic studies, including the discovery of the apolipoprotein E (APOE) gene variant E4, indicate that genetics play a significant role in the disease. Further research and genetic analysis may provide vital information for finding a cure for Alzheimer's disease, as the number of affected individuals is expected to rise dramatically with the aging population.