Final answer:
The preterite tense should be used for 'once upon a time' and the imperfect tense should be used for 'age'.
Step-by-step explanation:
The question asks whether the verb should be in the preterite or imperfect tense for the phrases 'once upon a time' and 'age'. In Spanish, the preterite tense is used for completed actions or events that happened at a specific point in the past, while the imperfect tense is used for ongoing or habitual actions or events that had no specific end point in the past.
In the case of 'once upon a time', this refers to a story or a specific event that happened in the past, so the preterite tense would be appropriate. However, for 'age', which refers to someone's age in the past, the imperfect tense would be used to indicate continuous or ongoing age. For example, 'Cuando era joven, tenía 20 años' (When I was young, I was 20 years old).