Why a longer trial pulls attention away
A "trial" here is simply one stretch of a task—say, watching for a target or holding something in mind until you respond. When that stretch is short, attention has little room to slip. When it is long, the same task gives the mind more empty time to drift toward unrelated thoughts. The 1997 experiment varied trial length and found that longer trials produced more mind-wandering [1]. That is a straightforward dose effect: more time on task, more drifting.
This is worth separating from the idea that some people are simply more prone to mind-wandering. The trial-length effect is about the situation, not the person. It says that the same individual will drift more in a long trial than in a short one, which is why researchers treat time-on-task as its own lever rather than a personality trait.
Age did not change the trial-length effect
The key result for the aging question is that the trial-length effect was not moderated by age [1]. In plain terms, older adults did not show a steeper rise in mind-wandering as trials lengthened than younger adults did. The effect of duration looked similar across the age groups tested.
That is a narrow but useful finding. It concerns how duration changes mind-wandering frequency, not whether older adults wander more or less overall. Other work has reported reduced mind-wandering propensity with age [2], so the overall level and the duration effect are separate questions. The duration result says the slope is similar; it does not settle where each age group starts.
What this means for the inhibition story
Inhibition-based accounts of cognitive aging propose that older adults have more trouble suppressing irrelevant thoughts and responses. If that were the main driver of mind-wandering during a task, older adults should lose the struggle against distraction more quickly as a trial drags on—their mind-wandering should climb faster with duration. The absence of an age-by-duration interaction is hard to square with that prediction [1].
The cautious reading is that this result counts against a strong version of the inhibition account, at least for mind-wandering measured this way. It does not prove inhibition plays no role in aging, and the study was designed to test the duration question rather than to measure inhibitory control directly [1]. A separate neurophysiological study examined time-on-task effects on mind-wandering across age groups but did not address inhibition-based accounts, so it cannot confirm or refute this interpretation [2].
The practical takeaway is that mind-wandering during a long task looks like a general consequence of sustained attention rather than a special vulnerability of older age. If you want to reduce drifting, shortening the task or breaking it into shorter blocks is the lever the evidence supports—and it should work about as well for an older adult as for a younger one [1].
Sources used in this answer
Aging and mind wandering: Reduced inhibition in older adults?
Longer trials increased mind-wandering, and this effect was not moderated by age; the paper discusses implications for inhibition-based theories of cognitive aging.
The Neuropsychological and Neurophysiological Signatures of Age-Related Differences in Mind-Wandering
The study examined age-related differences in mind-wandering using neurophysiological and behavioral measures, including time-on-task effects, and reported reduced mind-wandering propensity with age, but did not address inhibition-based accounts of cognitive aging.