In the first place the idea of the seven ages of man was not found by Shakespeare. This idea had been around for a long time, and finds its origin in a Latin phrase. Shakespeare was only the man to voice the idea, and in that he succeeded very well.
The number seven is probably derived from the seven sins. The number seven can be found several times throughout The Bible and can be seen as some sort of symbol.
If you would like to know more about the origin of this famous quote, I refer you to the Wikipedia page on the 'all the world's a stage'.
A justice is a judge.
It is from the comedy As You Like It.
Infant school boy lover soldier justice old age second childhood
He never said. Oh, he wrote the "seven ages of man" speech alright, but he did not say what its theme was.
"Shrunk shank" is the best.
Infant school boy lover soldier justice old man and death These are the seven ages of man as set out in a speech by Jaques in As You Like It.
In the "Seven Ages of Man", by William Shakespeare, the justice represents the stage where a person believes he has acquired wisdom. He is sitting back and relaxing.
In the words "The seven ages of man" there are seven syllables.
The infant is mewling and puking in his nurse's arms.
it is just saying that how the generation are changing day by day
It is pretty hard to describe them better than Shakespeare already did.