Actually Sita was brought at a very tender age in a box and given to Ravan by one of his friends.He opened it and seen that there is a just born girl in the box. His Guru informed him that if that girl lives in lanka with Ravana,there will be many problems and people will starve for food.Hence Ravana thrown it immediately into water. That box gone with waters and got embbeded in land.When Janaka is in his form, he found that box.
Hence people say that she was elder to Rama.
But the secong school says as long as sita was in the box there was no growth anh hence her birth date will be the date Janaka found her.Hence she was younger to Rama.
So importantpoint here is whether Rama is younger or older to Sita,their principels are so good and every one should follow.
Every couple should take these both as inspiration.They showed to the world that the greatest relation among all is WIFE AND HUSBAND relation.