One example of youth in the play 'Romeo and Juliet' by William Shakespeare is in the behavior of the young. It is also evident in their attitude to love. Romeo for example, has all the extreme moodiness and extremes of emotion that are common in youth - it is all or nothing with him. Looking at the way he loves at the beginning of the play, he fixates totally on Rosaline, being lovesick to the point of finding difficulty eating and sleeping. Then we have the fickleness and striving for novelty of youth - he changes his mind in an instant, preferring Juliet. He knows the difference and is convinced his love is different this time. Both are headstrong, impetuous and impulsive - and neither will take advice from their elders. Paris, and Juliet's father, do things with the perhaps turgid etiquette and protocal of the old - except that this show up Paris in a bad (uncool) light when compared to the passion and drive of Juliet's other suitor,Romeo.
To me, the best example of youth versus age is in Act II, Scene 3. In that scene, Friar Lawrence is talking to Romeo for the first time since Romeo has fallen in love with Juliet.
In this scene, Friar Lawrence is trying to talk to Romeo about Romeo's emotions -- he is trying to be a mentor to Romeo. When he finds out that Romeo has been out all night, he assumes it's with Rosaline. When he finds out that Romeo is in love again, he starts to try to reason with him. He cautions him about being hasty -- about falling out of love with Rosaline and back in so easily.
For much of the play, the old are no wiser than they young, but in this scene, we see a classic case of the older and wiser man trying to give advice to they younger one.
Romeo and Juliet are very hasty in their decision to marry so you could look ini Act II and find an example form when they are talking in Juliets yard.