Memory loss
Memory loss is common, as time takes a toll.
Heck, go in to a classroom in an infant's school and see what's left lying around in a break, and how much they've forgotten to pick up/take, and it's heartening to see that a poor attention span/concentration and poor memory's not just hitting the older adult!
As an adult with difficult memory that's not as bad as to be dementia, a term Mild Congitive Impairement (MCI) is used as a catch all for people with milder problems (and not severe enough to meet criteria for dementia).
Good news is that people with MCI often get better. In fact, most of them do. A study (by Ritchie, 2001) showed that overall 7 to 17% of people with MCI will still have it in a year's time. He showed if you've Parkinson's Disease too, then about 1 in 8 (12%) will develop dementia in the next year . . . but although 12% get worse and 7% to 17% stay the same, the remaining 71% to 81% get better.
In the absense of high risk factors like Parkinson's Disease, a study (Peterson, 1999) showed that only 0.5% of 70 year olds with MCI go on to develop dementia in the next year, rising to 3.9% of 85 year olds.
Bottom line is, having mild memory problems ain't that gloomy at all, and so often (in fact, almost always) will be 'old age' rather than a progressive dementia.