How were the individuals' baselines assessed? Some people have exceptionally good memories. It would not be suprising if these traits often persisted into old age in some of such individuals. For example a person with a savant pmemory at 25 might have the memory of an average 25 year when at 85. That would not suprise me. That said memory is not all that it is cracked up to be. When I was young I had an exceptional memory for facts. It hasn't helped me too much in adult life due to other psychosocial deficits and bad luck and evironment. There are different forms of memory. My emotional and autobiographic memory is sometimes so bad it is weird. Like many life events don't leave too strong an impression.