Question

Which lines in this excerpt from Shakespeare's Romeo and Juliet show that Lord Capulet thinks Juliet is too young to get married?

Answer 1

At one point, Lord Capulet says My child is yet a stranger in the world, which means that she is too young and has not experienced the world properly.

Answer 2

At the begining, Shakespeare writes, voicing the words of Juliet's father about the wedding with Paris:  

She is not yet fourteen years old;  

Let the two more lush summers die--  

Then Juliet can become his wife.  

That is, the Juliet's father clearly indicates that Juliet is too young to get married; Which says that and then it was not the norm, according to some.