Probably longer! There are many examples of grafitti dating back to Greek and Roman times, and the Egyptian pyramids are covered with grafitti. The origins of grafitti lie in the urge to make comment, political and social which has existed since civilised society itself. Greek and Roman philosophers and politicial commentators, famous and anonymous, were keen to leave their own particular opinion around for people to read, although they may not have realised how many people would read it, and for how long!
The art of grafitti has endured and evolved, but never really lost its original strength - the ability of the man in the street to make a comment and air an opinion in a lasting format, and last it has, for several thousand years.