There are many many reasons to lie about your age. Some of these reasons made perfect sense for me, many years ago. Fortunately, times have changed and I no longer desire or even need, to lie. It seems like just yesterday that JLW (formally known as JLA) and I were lying to a few 27-28 year old guys. We were 18-19 and 20 seemed so much better and older. So then, we were know as 20 year old's. If we has said 21, then they would have guessed we were lying (We can't get into bars!)
We used to meet up with our older fella's after the bars closed. I'd always be thinking "OMG, I am not going to bar's when I'm 28!" I thought for sure that I'd be married with a few kids and that I'd have no interest in getting wasted at 2am. Well, I was mostly wrong. No hubby or kids and I only stay out till 12:30! I really don't know how people my age can stay out drinking all night. Hangovers last me days instead of hours and I need to function on weekends. Forget about drinking all night and going to work the next day; I'd never make it there.
Looking back now, lying about our age seems silly. At least now, I can say that I'm 27 knowing that I barely look 21! Happy aging!