1. 少年
    A juvenile is a child or young person who is not yet old enough to be regarded as an adult.

    e.g. The number of juveniles in the general population has fallen by a fifth in the past 10 years.
           总人口中少年所占比例在过去10年中下降了1/5。

2. 少年的；未成年的
    Juvenile activity or behaviour involves young people who are not yet adults.

    e.g. Juvenile crime is increasing at a terrifying rate.
           青少年犯罪正在以惊人的速度增长。
    e.g. ...a scheme to lock up persistent juvenile offenders.
           将青少年惯犯关入监狱的计划

3. （行为）幼稚的，不成熟的，孩子气的
    If you describe someone's behaviour as juvenile, you are critical of it because you think that it is silly or childish.

juvenile

    e.g. He's a typical male, as he gets older he becomes more juvenile.
           他是个典型的男人，年龄越大越孩子气。

4. 幼仔；幼兽;雏鸟
    Young animals are sometimes referred to as juveniles .

juvenile