I don't agree that young people enjoy life more than older people do. I think enjoying life is not concerned with age but with understanding.
First of all, it seems that young people are not so worrisome as older people so that they can always free themselves to all kinds of joyment. But actually, in one hand, young people have their own questions such as "to be or not to be", they are tend to think about everything around them. That's why we have the nomination of Lost Generation and Beat Generation. In the other hand, do young people even know how to enjoy life?
So Secondly, sometimes older people who understand their being and being-there, just like what Heidegger suggested, may enjoy life more than young people. They have been through the scrub and elutriation of time. So they may want to have a break or a eternal state of freedom. Then they may truly enjoy their life instead of being sucked into the melancholia of Hamlet.
But finally, what is enjoying life? It's greatly connected with the understanding of what is life. Well, just like what Shakespeare said, now there is the rub. For we can dewell into a nutshell and call ourselves as the king in the world. But is enjoying more close to Stoic's ethics or Epicurus's pleasure? We know they are so different just as the enjoyment of a middleage Christian and a Max Weber's Puritan. So maybe after all, whether young people enjoy life more than older people do or not is not really a key towards the enjoyment. But the understanding of life and human being is the real trouble or we call say a sea of troubles.
As for modernists, I think who learns more about life and humanism, who may have a better possibility to get to enjoy life. But who want to live like Glaucon's state of swain, well whether being young or old, he may enjoy his life or not. But in a view of a philosopher, he is no more than a human who is closer than an animal rather than a god. So I don't really think that young people enjoy life more than older people do.