很多经历青春期的少男少女都曾感到莫名的情绪在体内躁动，甚至有些人会一时冲动而做出离经叛道的事。这是因为青少年是身体趋于成熟，而大脑发育没有跟上的一个时期。学者表示，对于青少年面临的独特健康挑战，我们的了解还远远不够，能做的也还有很多。

Whatever their foibles — door-slamming, grunting, excessive Snapchatting — teenagers are right about one thing: nobody understands them. This umbra of non-comprehension takes in not just parents, but doctors, psychologists, neuroscientists, social scientists, legal experts and educators.

不管他们有什么怪癖(摔门、不好好说话、把过多的时间花在Snapchat上)，少男少女们有一点是正确的：没有人理解他们。不理解他们的不只是父母，还有医生、心理学家、神经学家、社会学家、法律专家和教育者。

There is surprisingly scant scientific research about the hazy period between childhood and adulthood in which adolescents exist. As an editorial in the journal Nature pointed out this month: “A modern healthcare system without a focus on the unique challenges of paediatrics or geriatrics would be unthinkable, yet there is no similar effort on behalf of adolescents.”

有关青少年所处的介于童年和成年之间这段模糊时期的科学研究出奇地匮乏。正如《自然》(Nature)杂志不久前的一篇社评指出的那样：“难以想象一个现代医疗体系会不关注儿童或老年人所带来的独特挑战，但青少年没有得到类似的关注。”

The term adolescence stems from the Latin adolescere, meaning “to grow up” but, in many other contexts, it eludes easy definition. The World Health Organization puts adolescence between the ages of 10 and 19, with other categories jostling within that complex territory. The UN defines a youth as aged 15-24, a genre overlapping with “child” (under 18) and the generic “young people” (10-24).

“青少年”这个词来源于拉丁语adolescere，意思是“成长”，但在很多其他语境下，它不容易定义。世界卫生组织(WHO)把青少年定义为10至19岁，但涵盖这个复杂年龄区间的还有其他分类。联合国(UN)把青年定义为15岁至24岁，这与儿童(18岁以下)以及泛指的“年轻人”(10至24岁)重叠。

It should not surprise us, then, that there is great variation the world over — and even within countries — in the ages at which the young are entrusted with making adult decisions. Laurence Steinberg, a psychology professor, writes: “A society that tries 12-year-olds who commit serious crimes as adults because they’re mature enough to ‘know better’ but prohibits 20-year-olds from buying alcohol because they are too immature to handle it, is deeply confused about how to treat people in this age range.”

因此，我们对此就不应感到意外了：全世界(甚至各国内部)对于年轻人有能力做出成人决定的最低年龄界定存在巨大差异。心理学教授劳伦斯?斯坦伯格(Laurence Steinberg)写道：“我们把一位犯下严重罪行的12岁年轻人当作成年人来审讯，因为他们已足够成熟，应该‘知道什么事情不能做’了;与此同时，我们禁止20岁的人买酒，因为他们还不够成熟，无法驾驭酒精：这样一个社会对于如何对待这个年龄区间的人是深感困惑的。”

Biology provides an obvious pointer. Adolescence is thought to begin with the onset of puberty (sexual development), but patterns of puberty vary around the world — and within countries — over time. One study shows that in the mid-19th century, girls in developed countries had their first period at about 15 or 16 years old. By 2000, this had dropped to below 13, a trend that has been attributed to better nutrition and healthcare. Puberty also occurs earlier in boys. Childhood obesity is thought to be an accelerating factor.

生物学提供了明显的指标。通常认为，青春期(性发育期)开始时，儿童就成为了青少年，但发育的规律在全球(以及国家内部)各有不同。一项研究显示，19世纪中叶，发达国家女孩的初次月经年龄大约为15或16岁。到2000年，这个年龄降至13岁以下，这一趋势要归因于营养与医疗的改善。男孩的青春期也提前出现。据信，儿童肥胖是导致这种情况的一个因素。

Flowering bodies, however, are governed by childish brains. Prof Steinberg points out that the young brain continues maturing into the mid-20s. Neurodevelopmental changes depend partly on hormones and can drive pleasure-seeking, risky and impulsive behaviour. Accordingly, Professor Steinberg extends adolescence’s dominion to between the ages of 10 and 25.

然而，正在成熟的身体由仍处于孩童阶段的大脑控制着。斯坦伯格教授指出，大脑要到25岁左右才发育成熟。神经发育变化在一定程度上取决于激素，这些变化还可能激发寻求快感、冒险和冲动的行为。因此，斯坦伯格教授将青少年的年龄区间延长为10岁至25岁。

By then, of course, young people are already notching up the social milestones of adulthood: driving, voting, working, living independently, enlisting in the military, drinking, buying guns, marrying and becoming parents. Society will have long sexualised them. And for the digitally connected, the mis-steps of youth are today captured, shared and archived in perpetuity. That collision of adolescent brains with adult norms might underlie some of the darker statistics relating to young people. The leading causes of adolescent death are, respectively, road accidents, HIV and suicide.

当然，到那时，年轻人已经在完成标志着长大成人的一件件大事：驾车、投票、工作、独立生活、参军、饮酒、购买枪支、结婚和生子。社会应该也早已让他们具备了性别意识。对于成长于数字互联时代的人们而言，年少时走错的路如今会被记录、分享并永远储存下来。青少年的大脑与成年人的规范之间的冲突，可能从根本上导致了一些与年轻人相关的较沉重的统计数据。青少年死亡的主要原因分别是交通事故、艾滋病和自杀。

Adolescent health also deserves specific contemplation because the habits of youth can become the millstones of adulthood: teens who smoke cannabis or nicotine, or who abuse alcohol, often become hooked for life. Mental health issues tend to surface early in adulthood but afflicted adolescents are mostly diagnosed on the basis of adult criteria and treated with drugs intended for older patients. When it comes to understanding adolescents, it is adults who need to grow up.

青少年健康值得特别深思，还因为年少时的习惯可能会成为成年后的负担：抽大麻、抽烟或酗酒的青少年通常会终身成瘾。心理健康问题往往很早就有迹象，但青少年患者大多是根据成人标准接受诊断的，治疗所使用的药物也是原本针对年纪较大患者的。在了解青少年方面，需要成长的是成年人。