Hello All,
Just as a general reply to the OP, the pacing for each person is different. I have read a lot, and it was my personal experience, that taking a year off (at least) between Undergrad and Grad school is the way to go. Of course, this is not the end-all be-all so to speak. There are people in my program at MICA who are straight out of undergrad (one guy is only 21). Most of the people at MICA are on the younger side, myself included (I'll be 24 when I graduate in 2016.) At the end of the day, it is the strength of your work that is going to get you accepted, not your age.
Oh and I'll go ahead and point out that the dude that is 21 is making some of the strongest work in the program. You just have to be really honest with yourself once you are at the point where you're thinking of applying. Decide if your work shows the maturity of an artist ready to enter this more intense phase of your career; if you think it is, then go for it. If not, take a year and see if you are able to sustain your work, and start to learn to balance your "real life" with your "studio life". That aspect of time management/prioritizing is extremely useful once you arrive at Grad school.
Hope this helps