If you've ever watched a teenager click circles around you on a reaction time test, you've experienced the age decline firsthand. It's real, it's measurable, and it starts earlier than most people think. But the rate of decline is slower than the popular image suggests, and the spread between individuals widens dramatically with age — meaning what you do matters more than how old you are.
When does reaction time peak?
Around 17–19 years old. By that age, the nervous system is fully myelinated (the fatty insulation around nerve fibres that speeds signal conduction), dopamine systems are at peak activity, and synaptic density has stabilised at the adult-set level. Teenagers in this band routinely post simple visual RT scores of 195–235 ms — the fastest of any age group.
After about 24, reaction time starts a slow decline of roughly 1–2 ms per year. By 50, most adults have lost 25–30 ms relative to their teenage peak. By 70, the gap is closer to 70 ms. These are averages — the spread widens with age, which is the more important point.
What's actually slowing down?
Three things, and they each contribute roughly equally to the decline.
First, nerve conduction velocity drops. The myelin sheath around nerve fibres thins and degrades with age, which slows the speed at which signals travel. The effect is small — about 0.5 m/s per decade after 40 — but it adds up. A signal that took 80 ms to travel from eye to motor cortex at age 20 might take 90 ms at age 70.
Second, dopamine pathways weaken. Dopamine is the neurotransmitter that drives motor initiation and decision speed. Receptor density peaks in late adolescence and declines steadily thereafter. Lower dopamine means slower motor initiation — which is why older adults are slower on RT tests even when their nerve conduction speed is fine. It's also why Parkinson's disease, which destroys dopamine neurons, causes severe RT slowing.
Third, sensory acuity declines. The retina's rod and cone cells become less sensitive with age, which slows the initial detection of a visual stimulus. The lens yellows, which changes colour perception (especially for blues and greens). The pupil shrinks, letting in less light. Each of these adds a few milliseconds to the detection stage of RT.
Why the spread widens with age
Here's the encouraging part. At age 20, the spread between the fastest and slowest adults is about 80 ms (the 5th to 95th percentile runs from roughly 180 to 260 ms). At age 70, the spread is more like 150 ms (from 270 to 420 ms). The variance more than doubles.
This means chronological age becomes a weaker predictor of RT as you get older. A fit, well-rested, cognitively engaged 70-year-old can post scores that match a sedentary, sleep-deprived 30-year-old. The averages tell you what happens to the typical person; they don't tell you what will happen to you.
The Baltimore Longitudinal Study of Aging — which tracked simple RT across more than 2,000 adults over 30 years — found that the fittest quartile of 70-year-olds still posted scores under 280 ms, matching the typical 35-year-old. The least fit quartile was above 360 ms. Lifestyle was a stronger predictor than age.
What actually slows the decline
Three interventions have solid evidence for blunting age-related RT decline. None of them will make you faster than a teenager, but they will keep you closer to your younger self than the averages suggest.
Cardio exercise is the single most effective intervention. Regular aerobic training improves blood flow to the brain, increases BDNF (brain-derived neurotrophic factor), and helps maintain myelin integrity. Studies consistently show that older adults who exercise regularly post RT scores 20–40 ms faster than their sedentary peers. Effects show up after 4–6 weeks of consistent training and persist as long as you keep at it.
Action video games help too. The same visuospatial training effect that works for young adults works for older adults, possibly even more so. A 2022 study had adults aged 60–80 play CS:GO for 12 hours over 4 weeks; their simple RT dropped by an average of 18 ms. The training effect was specific to fast-paced action games — slow-paced games showed no effect.
Continued cognitive challenge — learning new skills, not just doing familiar ones — also helps. The key seems to be novelty. Doing crossword puzzles you've done for 30 years doesn't help much. Learning a new language, taking up a musical instrument, or mastering a new physical skill does. The brain stays plastic in response to genuinely novel demands.
What doesn't help
Brain training apps. The evidence is consistent: gains on the app do not transfer to general RT. Older adults who use Lumosity or similar apps for months show no improvement on independent RT tests. Save your money.
Supplements. The supplement industry markets heavily to older adults with claims about 'brain health' and 'cognitive support'. Almost none of these have evidence for RT improvement in healthy adults. The exceptions (creatine, omega-3s) show small effects only after months of consistent use, and even those are contested.
Passive relaxation. The idea that older adults should 'take it easy' is exactly wrong for cognitive health. The brain stays sharp by being challenged. Retiring to a life of television and gentle walks is a recipe for accelerated cognitive decline, including RT.
The bottom line
Your reaction time will slow with age. That's unavoidable. But the rate of slowing is much more under your control than the popular image suggests. The same things that keep your heart and joints healthy — cardio exercise, good sleep, continued learning, occasional novelty — also keep your nervous system fast. The 70-year-old who runs, games, and learns new skills will be dramatically faster than the 70-year-old who doesn't.
If you're past 50 and your RT score has crept up over the years, the most likely cause isn't age itself — it's the lifestyle drift that often accompanies age. Fix the controllables first. You'll be surprised how much comes back.