It would be difficult to argue that Romeo and Juliet aren't star-crossed lovers due to the fact that the Prologue and Choral interruptions purely state that they are; but if one were to write an essay for an assignment on it, look for the parts where Romeo thinks that he is using his free will to make choices. Also, Friar Lawrence must not believe in it either because he does so much to make sure that the two kids can be together. One could say that Romeo chose to go to the Capulet party and it was his choice to fall in love with Juliet at that time. One could even point out that Romeo chooses to fight against the stars by choosing to kill himself. In fact, he challenges the stars by saying, "I defy you, stars" (V.i.24). With that said, Romeo denies that fate has any control over him or his life. To Romeo, it is his decision to go to the Apothecary for the poison that he will use to choose to end his life. At no point do the stars say that Romeo will do these specific things, so one could say that he did them out of choice rather than following fate. The funny thing with fate, though, is she's still always right.
You might argue that Romeo has not the maturity to know if he wants Juliet or not. Until he meets Juliet, he insists that he loves Rosaline. Switching so quickly without knowing anything about Juliet also seems imature.
Romeo acts like boys I new in Middle School. Also, he acts like Tom Sawyer, who loves Amy, before he loves Becky.
Romeo? Star crossed? Not really! He's just a typical teenager