It all depends on the maturity level of the couple involved. However, the prevalence of divorce in our society has turned the institution of marriage into a more committed dating relationship. People aren't willing to stick it out and work out their problems anymore. Marriage is HARD WORK, and (in general) our society has degenerated to the point that we believe we can just toss something away if we don't like how it works. For me personally, I would never request a divorce (assuming I get married) unless my wife was physically/mentally abusive to me and/or my family or children, or cheated on me.
For me? Well, if I can get hitched by the time I'm 25, I'll be happy.
Ryan