Well, some of my friends didn't save at a young age because they wanted to enjoy their youth, many people who aim to have investments at a young age they're hoping their investment can give a financial freedom when they're retired. My friend said youth only happens once in a lifetime so they want to enjoy it without any regret because they miss their youth. As long as we can maintain our spending so we won't have any debt I think it's people choice.
Your friend is totally wrong, he doesn't understand about the investment purpose. Although we invest in the young age, it doesn't mean we ruins our youth. We don't invest all our money, we just spend the money that we afford to use for the investment. Sure, there should be some amount of money we use to enjoy the youth. We know that we must keep everything in right way, including about allocating the money for our needs. People can choose to enjoy their young age, but they don't forget to prepare their old ages.