The study focused on ice hockey players
People concussed in their youth show subtle signs of mental and physical problems even more than 30 years later, say Canadian researchers.
The study, published in the journal Brain, found athletes with a history of concussion had worse physical and mental test scores.
The researchers stressed these minor changes did not affect day-to-day life.
Experts said minor head injury recovery could be slow, but this was the first hint of a longer-lasting effect.
The small-scale study involved just 40 former athletes aged between 50 and 60, 19 of whom had a history of one or more concussions in their youth.
The researchers from Montreal University carried out a battery of tests, covering everything from short-term memory and the ability to follow simple verbal and written commands, to motor control.
The previously concussed volunteers had poorer performance in the memory tests, delayed responses to unpredictable events, and were unable to complete the hand control tests as quickly.
Dr Louis de Beaumont, who led the study, said: "This study shows that the effects of sports concussions in early adulthood persist beyond 30 years post-concussion, and that it can cause cognitive and motor function alterations as the athletes age.
"Athletes should be better informed about the cumulative and persistent effects of sports concussion on mental and physical processes so they know about the risk associated with returning to their sport."
However, he said there were no signs of more serious problems such as Alzheimer's and Parkinson's Disease, and despite the test results, the former athletes were all healthy, maintaining a "very active lifestyle".
Further studies would be needed, he said, to see if the effects linked to concussion worsened as people aged even further.
Luke Griggs, from brain injury charity Headway, said: "It is encouraging to see research being carried out on the long-term effects of concussion and, as far as we're aware, this is the first study of its kind.
"It would be interesting to see if these effects were related to the way that the participants' head injuries were managed at the time as we know that this can make a big difference to the outcome over a shorter period.
"While some minor head injuries can result in no problems, others can cause sustained problems over several months and too many people are discharged from hospital after minor head injuries without being given sufficient information on the potentially long-term effects."
Andrew Scheuber from the Alzheimer's Research Trust said: "Sportsmen and women should take extra care to avoid head trauma.
"Some experts believe that footballers from the 1970s and earlier, including Danny Blanchflower and Billy McPhail, may have developed dementia as a result of heading old-style heavier footballs - though this is open to debate.
"Much more research is needed if we are to minimise dementia risk for everyone."