Final answer:
The correct preterite verb is 'estuve'.
Step-by-step explanation:
The correct preterite verb to complete the sentence is estuve. The sentence is talking about a specific event in the past, which is the time the speaker spent in Spain when they were fourteen years old. The verb estuve (I was) is used in the preterite tense to indicate a single completed action or event in the past.
Learn more about Selection of correct verb tense