While things can vary a great deal couple to couple, in general, decisions with ideally lifelong benefits and consequences are not the sort to be taken lightly. I married prior to the age of 30, and I don't regret that decision, but my hand was largely forced by immigration law. If I had not had that external push to marry my then girlfriend or have our relationship over a distance of 2500 miles, I likely would not have proposed until into my 30s, because a decision that impacts the remainder of your life significantly is not one to take lightly.