There can a wide range of 'normal', as everyone is different. We all have cognitive strengths and weaknesses. We also fluctuate in our cognitive performance to a degree. If there is an enduring change for the worse, however, this may be a cause for concern.
One of the big questions I am often asked what is normal as you get older. We do know that certain changes occur cognitively, and these are to a degree mirrored by changes in the structure and function of the brain.
Most obviously, our speed of processing tends to decrease as we get older. This means it takes us longer to bring things to mind and to think through matters. Given time, however, we tend to be able to remember, at least the broader details.
There is also some decline in memory function - it can be harder to remember all the details of events and interactions.
In addition, our so-called "executive skills" do tend to diminish as we get older. This means we may have increased difficulty solving more complex problems and engaging in more tasks that have multiple components or require timing and sequencing.
With age alone, however, we do not expect a significant deterioration in our language skills (though we may have a slight increase in difficulty bringing words to mind). Likewise, we do not expect a significant decline in our visuospatial skills - these allow us to know where we are in space and in relation to other things around us. Problems in these areas are a reason to seek help from a professional.
The other aspect of "normal cognitive ageing” is that the deterioration in our cognitive skills should not cause major impairment of our ability to function day to day. We may need to compensate for instance, using diaries or calendars more often - though we should be able to manage our daily affairs. If this is not the case, again this should be a reason to seek help.