I've long believed that the apparent 'speeding-up' of time has simply got to do with the percentage of your life any given period represents. For example, the year between your 9th and 10th birthdays involves 10% of your life to date, which is quite a large chunk. On the other hand, the year between your 49th and 50th birthdays involves only 2% of your life to date, which is a relatively small chunk. It may well SEEM, therefore, to have passed five times more rapidly than than the earlier year.