Well, clearly the speed with which Juliet "falls" for Romeo is indicative of a certain level of impulsiveness. Juliet is a young woman who knows her role and station and what is expected of her. She would have known that she would not have been able to choose who she could love and who she could marry. Daughters of upper class families in those times were expected to make alliances, not to marry for love. And yet, when she first sees Romeo in Act I scene v, she is impulsive in the speed in which she falls in love. Note what she says to her Nurse when inquiring about the identity of her mystery lover:
Go ask his name.--If he be married,
My grave is like to be my wedding bed.
Already, after this one meeting, Juliet is thinking in absolute terms. She is lot letting reason restrain her emotion and passion. In the same way, when she finds out the identity of Romeo, she says:
My only love, sprung from my only hate!
Note the absolute terms that Juliet uses here. Already, for a young girl who has probably never loved before, she refers to Romeo as her "only love" and seems to pledge herself only to him, without knowing hardly anything about his character apart from the fact that he kisses "by the book." She shows herself as incredibly impulsive and governed by emotions rather than by reason.