There's plenty of time: the time you waste by not spending money you don't have. You have to wait longer until you make more money in order to spend more without interest.

Don't spend money you don't have. Especially don't do it with 20% interest short-term loans. It's not that hard. If you're not financially responsible enough to handle a credit card, do not get one. I didn't have one until my late 20s.