Quarter life refers to reaching the age of 25.
As in welcome to the quarter century club, a quarter of your life has expired and you have entered the quarterlife crisis. This is about the time you start to realize the clock is ticking. You may have applied yourself 100% to get exactly where you are and perhaps suddenly, perhaps gradually, come to feel it is truely not where you really want to be or who you have become.
by Dogwalker March 11, 2008