I'm 23 (turning 24 in March). I will have 3 years of work experience when (if?) I matriculate in the Fall of '08.
I think it's all about Why now? You have to show adcoms why you need to back to school now and can't wait a few years. You also have to show the adcoms that you know what your future short-term and long-term goals are. If you don't have clear goals, then it's obvious you need more time to mature.
I think it's important to stress in your essays, recos, and GMAT score that you are mature enough and ready to earn an MBA. Are younger people at a disadvantage? Perhaps, but it's not an impossible hill to climb if you put together a good application package. IMO, the age isn't as much of a concern as the zero work experience,