The fact that older adults sometimes have difficulty with the processes of executive functioning can be explained by:

Executing functioning is your mental ability of organizing your thoughts which is transcended to your motions. This includes time management skills, multi-tasking, ability to concentrate, memorization skills and the like. The part in the brain that is responsible for this is the frontal lobe. The information sent to the brain are passed by neurons through linkages called synapses. These synapses are electrochemical signals that flow through your brain in order to do its functions. For adults, DNA replication is starting to get slow. As a result, more of the neurons die while there is slow production of new neurons. Hence, there are space gaps in the brain of adults. That's why the information that travels through signals takes a while to get through. Hence, adults tend to be more forgetful and unmindful of their actions.