It requires a bit of context that many people don't have anymore. World War 1 wasn't just hideously destructive, it irrevocably changed our culture. Before WWI, people still had what we consider to be old fashioned notions of honour, chivalry, very traditional gender roles and so on.

Entire villages and neighbourhoods send all their men into WW1 with thoughts of chivalry in combat. And WW1 ground them up like a meat grinder and spat the maimed remnants of the survivors back out.

WW1 was a war fought by people with old fashioned notions but industrialised weaponry. It is hard to understate how horrific it was. Not just for the combatants but also for the survivors and the people back home.

It resulted in what they called the lost generation. A generation of people who felt absolutely no connection with the culture from before the war. Heroism, honour, chivalry, propriety, how meaningless it all seemed after the horror of WW1 put the lie to it all.

The lost generation, in the eyes of their elders, was a generation without any aim in life. A generation that just drank and partied and fucked and generally wandered their way through life without any of the traditional goals like maintaining ones reputation, finding a spouse and starting a family and career.

The protagonists in this novel are part of the last generation. And what Heinlein is doing is nuancing that opinion of the lost generation as a bunch of godless wastrels.

He's depicting them as people who had the illusion ripped away from the world was WW1 exposed the lie behind their society. It doesn't make them wastrels. It made them people on a quest to give new meaning to their lives.

So yeah, they travel, party, drink and fuck around. Their whole world was destroyed and now they have to figure out for themselves what their new values and goals are. And yes, that can make them look aimless and pointless as they indulge themselves to figure out what they want for themselves and from each other.

For me, that context makes the book feel oddly contemporary because it's a state a lot of young adults find them in today as well. A world that changes so rapidly, with many people being migrants who don't entirely share their parents culture. We're all just drifting, trying to figure out what we want our lives to be.