It really starts when I was 18 and got a job at Macy's. I got a card to help build my credit, and also so I could "afford" work clothes. A friend told me that "you can't build credit with a department store card", so I applied for several "student" cards.
I was doing all right with keeping my balances low, until I left for school in another state.
All of a sudden I'm on my own, responsible for rent, power, water, gas, food, AND phone. It was an eye opener to say the least. I enjoyed being a "grownup", but I found it hard to afford the basics on a part time minimum wage job.