Even though they were both teenagers, it was necessary. To stop the Uchiha clan's plan to turn against the village and in return have the Hokage get rid of the Uchiha. One of the most talented Uchihas, son of the head of the Uchiha clan, and you, the granddaughter of the Hokage himself, had an arranged marriage.

A few days after all the formalities were completed, Itachi and you were officially married, which wasn't exactly great for either of them.