Though Juliet is of an age that can choose to act immature or mature, at the play's beginning she seems an obedient, sheltered, naïve child. An example of this comes when her mother asks to see her:
“Madam, I am here, what is your will?”
This seems to be an almost subservient manner to approach someone calling for her.
Although many girls her age, including her mother Lady Capulet, were almost forced into marriage; Juliet has not given the subject any thought:
“It is an honour that I dream not of.”
When Lady Capulet mentions Paris' interest in marrying Juliet, Juliet dutifully responds that she will try to see if she can love him; a response that seems childish in its obedience and in its immature conception of love. Lady Capulet does not seem to think that it is an extraordinarily important thing, and seems to want to spend only a small amount of time on the subject:
“Speak briefly, can you like of Paris’ love?”
Juliet does not seem comfortable talking about sex ,as seen in her discomfort when the Nurse goes on and on about a sexual joke at Juliet's expense:
‘”Yea”, quoth he, “dost thou fall upon thy face?/ Thou wilt fall backward when thou hast more wit.’
Juliet gives glimpses of her determination, strength, and sober-mindedness, in her earliest scenes, and offers a preview of the woman she will become during the five-day span of Romeo and Juliet:
“I’ll look to like, if looking liking move;/ But no more deep will I endart mine eye/than your consent gives me strength to make it fly.”
This shows Juliet’s current immaturity to love, as she thinks only of the physical attributes of the County Paris. In addition, even in Juliet's dutiful acquiescence to try to love Paris, there is some seed of steely determination. Juliet promises to consider Paris as a possible husband to the precise degree her mother desires. While an outward show of obedience, such a statement can also be read as a refusal through passivity: Juliet will accede to her mother's wishes, but she will not go out of her way to fall in love with Paris. This shows a certain independency which cannot come through obedience.
Juliet's first meeting with Romeo seems to inspire a further realisation of this independence and the adult-hood that comes with it. Though profoundly in love with him, Juliet is able see and criticize Romeo's rash decisions and his tendency to romanticize things, an example comes when he wishes to describe how he got into the Capulet orchard:
“With love’s light wings did I o’erperch these wlls,/ for stoney limits cannot hold love out.”
This is a typical, carried-away-with-love statement, however, Julkiet’s reply, seems more level-headed and mature approach to Rome’s intrusion:
“If they do see thee, they will murder thee.”
After Romeo kills Tybalt and is banished, Juliet does not follow him blindly, like a grieving lover, she makes a logical and heartfelt decision that her loyalty and love for Romeo must be her guiding priorities. Essentially, Juliet cuts herself loose from her prior social engagements, her parents, her social position in Verona and her nurse in order to try to reunite with Romeo:
“Thou and my bosom henceforth shall be twain.”
When she wakes in the tomb to find Romeo dead, she does not kill herself out of feminine weakness, but rather out of an intensity of love, just as Romeo did.
Juliet's suicide actually is a more daring, and hence more demanding one than Romeo's because he swallows poison, she has to stab herself through the heart with a dagger:
“O happy dagger,/This is thy sheath;/there rust, and let me die.”
Juliet's development from a wide-eyed girl into a self-assured, loyal, and capable woman is one of the most interesting characteristics of the play. It shows how, facing the circumstances of love and death, children, as she is little more than a child, can shine through and display tremendous levels of courage, level headedness, and maturity. Throughout the play, Juliet has to deal with death, not only of her love, but of her cousin Tybalt, and does not sway into depression, like any over hormonal teenager. When faced with love, she is not blinded by sheer lust, but thinks of causality and is engulfed in rational thought. These aspects of her personality shine through, giving the reader the overall impression of a mature woman.