No it's not advisable, it's risky. After only 3 or 4 months you probably don't know the real charater of the other person (they may still be on their best behaviour). And it's hardly even enough time to plan a wedding. But when it comes to love and matters of the heart things like time, age, distance, past history etc don't matter. It won't be the same time-frame for everyone, but 3 or 4 months seems too soon.