That's actually a sort of tricky question. While I'm not an attorney and can't give out legal advise, it's my understanding that legally, the debt is still owed unless it was satisfied regardless of how much time has passed. At the same time, different states have what's known as a "statute of limitations" for how long creditors may wait to act upon collecting said debts through the court system and/or other means.
What that means in a nutshell is; technically a debt lasts forever, but in most states after a certain number of years, there's not much they can do about collecting it.
That's certainly not to say you should try to 'squat out' your debts by avoiding creditors - regardless of where you live it's a significant amount of time before the statute will apply - and there's lots of other ramifications to your credit as a whole in the meantime.