For many people time seems to run faster as they get older. That is, for an old person an hour, a day or a year seems to be shorter than for a young person.

Is there any hard data for such phenomenon? And if so, what is the cause?

To name a few possibilities it can be about the reaction time (so one have more or less 'turns' in a minute), the relative time comparing to one's age, ways in which memory changes with age or habits (younger may live more active life). Of course, there may be different causes for different time scales. However, I haven't found anything but anecdotal data and home-made theories.