If people can change, they tend to only do so superficially.
Deep down, they tend not to change. They can, but it takes a lot more effort. What I am saying, is that your friends were likely to some extent destined to become layabout sods in their late teens, maybe early twenties. I say this bearing in mind that a person's personality tends to develop up until the age of about 25, and it undergoes it's greatest development during early years in childhood, which will fundamentally shape your subconscious thinking, social skills, attitude, worldview, ethics and personal values. By the age of 20-ish, those are mostly fully developed.
Sometimes it just takes some time for those personality traits to manifest their consequences in adulthood. You start to see those in their late twenties. But the underlying personality traits were likely always there.
People can change bad habits, but it's difficult and relatively rare. According to one source I read, it apparently takes approximately 7 years to repattern your mental state and change your attitudes on a fundamental level. Even that, I am skeptical of, as I have seen no evidence of it yet in real life. I don't remember where I read that either. Majority of literature on personalities suggests that they do not really change at all beyond the age of 25-30. At best, people learn how to control their flaws and insecurities better with age, so they can lead slightly more productive and successful lives. That's all.