This is a confusing question to me: what are his thoughts on their attitudes? It seems to me what he thought about them is best expressed in what these characters say and do and how they feel. Unfortunately for them, what they say and do is based primarily on how they feel. While that may be true for all of us to some degree, a little more age and experience would probably have avoided the fights and the rash and permanent decisions all the young people in this play made--and which ultimately caused so much violence and death.
Perhaps Shakespeare would agree with Irish literary critic, playwright and essayist, George Bernard Shaw. who commented, "Youth is wasted on the young." For, it seems that Friar Laurence voices this sentiment for his author.
The tragedy of these young lovers derives from their youth. While the intense passion and desire that Romeo and Juliet have for each other has an inspiring beauty to it that touches the spirit of all who read or view this play, it is tragically spoiled by their youthful impetuosity. Older, with some temperance, the love of Romeo for Juliet could have been one of the enduring loves of their times. Indeed, "these violent delights have violent ends."
Shakespeare was an extraordinary observer of his fellow men, women, and children. It is interesting to note that he wrote Romeo and Juliet when his daughter, Judith, was fourteen. Suzanne was two years older so he had already observed it once before.
In the characters of Romeo, Juliet, Mercutio, Tybalt, Paris, and Benvolio, he perfectly captured that paradox we call teenagers.
Both Romeo and Tybalt are ruled by their passions. They act before they think. If they were to think before they acted, they probably wouldn't have died.
Tybalt hates with a passion that is abnormal. He always seems to be angry and ready to fight even knowing the consequences, he doesn't care. He has not learned how to keep his emotions in check and thus he is ruled by them.
Romeo is also ruled by passion, love. In the beginning, he just thinks that he is in love and enjoys being self indulgent about his unrequited love. He revels in it. Then he sees Juliet and is attracted to her instantly despite the fact that they are masked. Their shared sonnet shows that they get each other. They complete each other. When Romeo hears from Balsasar that Juliet is dead, he immediately leaps to the idea of suicide. He doesn't go to Friar Laurence, his confident, to find out what happened. Romeo is impulsive.
Juliet behaves exactly like a typical teen age girl who has just become a woman. Juliet is the practical one. But she is also an emotional yo-yo. Feeling new and deep emotions for the first time is powerful. Juliet embraces her new found love in Romeo, but when everything starts to go wrong and she goes for help from Friar Laurence, we see her desperation. Just before she takes the sleeping potion, she wavers. Her emotions are going wild.
Mercutio is also a typical teenage male. He is the jokester of the group and his main topic is sex.
Paris is a young man in love but unlike Romeo, he seems to have his emotions under control. Since he really doesn't know Juliet, he isn't as emotionally invested.
Benvolio is the level headed one. Each group should have one. He is the peacemaker. He tries to stop fights rather than start them.
In any group of teenagers you will find a mixed bag of personalities. Shakespeare managed to capture many of them in his group of teenagers in Romeo and Juliet.
If we judged his attitudes from what is given in the drama, I think that we can make the argument that he viewed young people as being able to represent a range of emotions. Some of these are rooted in passion, yet can bring about painful conditions, while others are embedded in being able to scheme and plan extremely well. In Romeo, we see Shakespeare's belief that young people are capable of a reservoir of emotion. Romeo is shown to be brooding, pain ridden, and then elevated to a level of complete awe and love when first seeing Juliet. He is enthralled with her and acts with her emotional frame of reference imprinted onto his own. In Juliet, we see another side to what it means to be young. She is more of a very shrewd and smart youth. While she feels emotion and is very emotional about Romeo, she understands that, as a woman, her lot to bear is more fraught with challenges and not one that lends itself to an extreme level of displaying emotions as Romeo. Juliet is the one who has to deceive, analyze angles of perception, and develops the plan for them to escape. In showing the main characters through such lights, Shakespeare might be making a statement about what it means to be young and the different dimensions youth carries within it.