We are told in the play that Juliet is not quite fourteen, which means she stands on the cusp between childhood and adulthood. When we first meet Juliet, she is presented as an immature, obedient child, who obviously has not thought much about marriage, and says to her mother that she will try to love Paris. She is also uncomfortable with the Nurse's repeated references to sex. She also, however, shows her determination and resolute nature in these first scenes. She is able to quiet the nurse with a word in Act I scene iii where her mother is unable to quiet the nurse, and in her response to her mother there is a note of passive resistance.
It is when she meets Romeo that Juliet takes a definite step towards adulthood. Although she is head-over-heels in love with Romeo, she is still able to maintain an objective stance and criticise Romeo for his tendency to romanticise their love and for his rash decisions. After Romeo's banishment, she makes a rational decision to take her union with Romeo as her new focal point and to make all other decisions based on this. It must have taken a lot of courage for her to reject her parents and former social position when everyone was encouraging her to marry Paris and keep her marriage with Romeo a secret, yet in her choices and her daring in taking the potion of Friar Lawrence we see a steely determination and resoluteness that is completed in her decision to end her life because of the intensity of her love for Romeo. In this play therefore we see the development of a young child into an eminently capable, strong and resourceful woman.