Two things imo:
1) When we're 5y/o a year is 1/5th of our life - a long time. At 40 a year is 1/40th, not long.
2) Constant instant communications. TV, internet, cell phones - a constant awareness of time passing quickly because there's so much information being constantly updated and which some people feel they need to constantly absorb. In the 'olden days' we caught up with friends once a week or so, a 'long time' by today's standards. A letter to a foreign country used to take a month to get a reply to and now with email it's nearly instant. We've created a society that is no longer able to sit still and/or occupy itself, always running around for the next distraction and then claiming 'there is not enough time in the day'. Get rid of all technology and go camping old-style in the wilderness for a week and then tell me whether you still think that 'time is moving fast'