The younger waiter is just your typical young guy. Unlike the older waiter and the old man, he thinks that life is full of value. Also unlike them, he has a wife waiting at home, and he can't wait to get back to her after work. He values time highly – in his view, every hour is precious and ripe with promise. We can sympathize with him; after all, who doesn't want to stay young forever? To him, old age is pathetic and revolting, an attitude reflected in his condescending attitude towards the old man.
The younger waiter is unsympathetic to the loneliness and despair of the old man; as a young guy, he doesn't feel his own mortality yet, and can't comprehend the nothingness that both the old man and the older waiter seem to feel. While the younger waiter is quite rude (and cheeky!), we don't get the feeling that he's a bad guy – rather, he's naïve and ignorant of the true nature of the world. We can't help but think that Hemingway is making a point about the brashness of youth in general here – the young waiter thinks he's invincible, and that the universal problems of old age and death can't touch him. However, while he is young and confident now, the implication is that once he hits a certain age and starts to feel life slipping away from him, he'll be just like the older waiter and the old man.