Most people who develop dementia are 65 or older, and the risk rises steeply with each passing decade. Among adults 65 to 74, about 1.7% have a dementia diagnosis. That jumps to 5.7% for those 75 to 84 and 13.1% for people 85 and older, based on 2022 CDC data. But dementia is not a single disease, and certain types strike much earlier.
How Age Affects Your Risk
Age is the single strongest risk factor for dementia. After 65, your risk roughly doubles every five years. By the time people reach their 90s, the numbers are striking: over 40% of adults aged 90 and older have dementia, according to the long-running 90+ Study at the University of California, Irvine.
That said, dementia is not an inevitable part of aging. The majority of people in their 70s and early 80s never develop it. Many people live into their 90s with their cognition largely intact. The doubling pattern means age dramatically increases your odds, but it doesn’t guarantee anything.
Alzheimer’s Disease: The Most Common Type
Alzheimer’s accounts for the largest share of dementia cases, and for most people it’s a disease of the mid-60s and beyond. Symptoms in the late-onset form, which is the typical variety, first appear in the mid-60s or later. Memory loss is usually the earliest sign, followed by increasing difficulty with planning, conversation, and daily tasks.
A small number of people develop early-onset Alzheimer’s before age 65. This form can begin as early as a person’s 30s, though that is rare. Three specific inherited gene mutations are responsible for many of these cases. A person who carries even one copy of a mutated gene will likely develop Alzheimer’s before 65. If you have a parent or sibling who was diagnosed unusually young, that family history is worth discussing with a doctor.
Frontotemporal Dementia: Often Strikes Earlier
Frontotemporal dementia (FTD) stands out because it hits people at a younger age than most other forms. About 60% of people with FTD are between 45 and 64 when they’re diagnosed. Rather than memory loss, the first signs often involve personality changes, impulsive behavior, or difficulty with language. Because it appears during peak working years, it’s frequently misdiagnosed as a psychiatric condition before the true cause is identified.
Lewy Body Dementia: Onset at 50 and Beyond
Lewy body dementia typically begins at age 50 or older, though younger cases occasionally occur. Early symptoms can look quite different from Alzheimer’s. Visual hallucinations are common and often appear early. Changes in mood, sleep, vision, and even bowel function can precede the more recognizable cognitive decline. One distinctive feature is REM sleep behavior disorder, where a person physically acts out dreams. In some people, this sleep problem shows up years before any other symptoms of dementia.
Vascular Dementia: Tied to Heart and Stroke Risk
Vascular dementia results from reduced blood flow to the brain, most often caused by stroke, hardened arteries, or heart disease. Because those conditions become more common with age, vascular dementia is primarily a disease of older adults. Symptoms can come on suddenly after a stroke or develop gradually over time, and they tend to worsen in a stepwise pattern with each new cardiovascular event.
There is one notable exception. A genetic condition called CADASIL causes vascular-type dementia with symptoms that can begin in a person’s mid-30s, starting with severe migraines, seizures, or depression before cognitive decline sets in.
A Recently Identified Type: LATE
Researchers characterized a form of dementia called LATE (limbic-predominant age-related TDP-43 encephalopathy) in 2019. It’s estimated to affect about one third of people over 85. LATE causes memory problems that closely mimic Alzheimer’s, which makes it difficult to distinguish between the two without specialized testing. It frequently occurs alongside Alzheimer’s pathology, meaning some older adults may have both conditions simultaneously. New clinical criteria now help doctors differentiate LATE from other dementias.
Earlier Detection Is Improving
Blood tests for Alzheimer’s have advanced significantly. A commercially available test measuring a specific protein called p-tau217 can now detect Alzheimer’s pathology at all stages, including before symptoms appear. A newer version of this test, called PrecivityAD2, combines two protein measurements for even greater accuracy. These tools are especially useful for people in their 50s or 60s who notice subtle cognitive changes and want to know whether something more serious is developing.
For primary care settings, a quick cognitive screening tool called 5-Cog can be completed in about five minutes when a patient or family member raises concerns. It was designed to work across cultural backgrounds and automatically flags results in the patient’s medical record if follow-up is needed.
What Determines Whether You’ll Be Affected
Age is the biggest factor, but it’s far from the only one. Cardiovascular health plays a major role across nearly all types of dementia. High blood pressure, diabetes, smoking, obesity, and physical inactivity all increase risk. Hearing loss, social isolation, depression, and lower levels of education have also been linked to higher rates of cognitive decline.
Genetics matter too, but less than most people assume for the common late-onset forms. Outside of the rare inherited mutations that cause early-onset Alzheimer’s, carrying a risk gene like APOE e4 raises your probability without making dementia certain. Lifestyle factors, accumulated over decades, appear to account for a meaningful share of cases. Some researchers estimate that up to 40% of dementia cases worldwide could theoretically be prevented or delayed by addressing modifiable risk factors throughout life.
The practical takeaway: dementia is overwhelmingly a condition of older age, with risk climbing most sharply after 75. But certain types, particularly frontotemporal dementia and inherited Alzheimer’s, can appear decades earlier. Paying attention to cardiovascular health in midlife is one of the most effective things you can do to lower your risk in the decades ahead.