He is less than 40 years old.
8. enough修饰名词时，在名词前后都可以。
They said that they had enough food.= They said that they had food enough.
 enough 修饰形容词和副词，位于其后。
 He is old enough to join the army.
 He isn’t old enough to go to school.
9.形容词else通常放在疑问代词，疑问副词或不定代词后
 what/who/where/when/when else
 something/anything/nothing…else
 What else did you do?
 Do you have anything else to say?
10.由两个或两个以上的词组成的形容词词组修饰名词时须放在名词之后。
This is the book easy to read.
这是一本容易读的书。

形容词知识拓展:
名词化的形容词：
有些形容词可以和定冠词连用，表示一类人或事物，这时，它相当于一个名词，可作主语或宾语；
表示一类人时，看作复数，表示一类事物时，通常看作单数。
Robin Hooh(罗宾汉) hated the rich and loved the poor.
The old are taken good  care of in American.
the+形容词，常见的短语有：
the old/the young/the sick/the white/
the black/the rich/the poor/the dead(死者)

形似副词的形容词：
以-ly结尾的词通常是副词，但是下列词为形容词。
friendly  lonely (孤独的) ；lively (活着的)；lovely(可爱的)

复合形容词的类型：
(1)名词+过去分词  man-made satellite 人造卫星
(2)形容词+现在分词  a good-looking man
(3)形容词+名词  second-hand cars
(4)数词+名词-ed   three-legged chairs三条腿的椅子
(5)数词+名词  400- metre race
(6)副词+现在分词  hard-working students
(7)副词+过去分词  well-known writers
(8)形容词+形容词  a dark-red jacket
(9)形容词+过去分词  ready-made clothes 成品服装

含有形容词的常用句型：
(1) It’s+adj. of sb. to do sth.
(good/ kind/nice/polite/clever/foolish… )
It’s very kind of you to help me.
(2) It’s +adj. for sb. to do sth.
(difficult/easy/hard/dangerous/usefulinteresting/important…)
It’s important for us to learn English well.
(3)下列形容词后常跟动词不定式
 表示情感或情绪的形容词：glad,pleased,sorry,sad,afraid,thankful…
 I'm glad to see you.
表示能力，意志或推测的形容词：ready,able,sure,certain…
 I’m sorry to hear that.

某些现在分词和过去分词可作形容词
the moving story 令人感动的故事
a moved boy   一个被感动的男孩
a frightened child 一个被吓到的孩子
a frightening film 一个恐怖电影