我觉得应该用Sahira was five, 标点不太确定. 豆包也认为应该用 was ,还给加了and.
The first part "Sarah had been five when Tom was captured" uses the past perfect tense "had been". The past perfect tense is used to show that one past action happened before another past action. But in this case, just using the simple past "was" would be more appropriate for the first clause because there isn't a clear sequence of past events where one past action needs to be emphasized as having occurred before another in terms of the relationship between Sarah's age and Tom's capture. A more natural way to say it would be "Sarah was five when Tom was captured, and she was twenty-three when he was released."

完整的两个并列句需要连词，
但是两句中相同的部分可以省略掉，可以省略连词、主语、谓语等等，意思表达更简略流畅，这里and也省略了