为了简化事情，您可能应该将您的年龄设为 Integer 或 int 而不是 Sting，但由于您的问题是关于 String age 这个答案将基于 String 类型.

To simplify things you should probably make your age Integer or int instead of Sting, but since your question is about String age this answer will be based on String type.

假设 String age 持有表示整数范围内值的字符串，您可以简单地将其映射到 IntStream 并使用它的 IntSummaryStatistics 之类的

Assuming that String age holds String representing value in integer range you could simply map it to IntStream and use its IntSummaryStatistics like

IntSummaryStatistics summaryStatistics = testList.stream()
        .map(Test::getAge)
        .mapToInt(Integer::parseInt)
        .summaryStatistics();

int max = summaryStatistics.getMax();
int min = summaryStatistics.getMin();