How long until my credit history is considered to be "a long time"?

From myfico.com

“Length of Credit History (15% of your score)

* Time since accounts opened
* Time since accounts opened, by specific type of account
* Time since account activity

Length of Credit History Tips

* If you have been managing credit for a short time, don’t open a lot of new accounts too rapidly.
New accounts will lower your average account age, which will have a larger effect on your score if you don’t have a lot of other credit information. Also, rapid account buildup can look risky if you are a new credit user.”

5–7 years for at least with 3 open active trade lines with high balances or limits over $7500.

Some advice I learned the hard way. If you pay off a credit card because you don’t want it anymore, don’t close the account. Just keep it open but don’t use the card. Closing the account will also cause your score to drop.

I’ve had good credit for about six years, and when I started ten years ago, my credit score was around zero. Now my number is around 650 out of 850. Just be consistent with payments and don’t get in default, and don’t miss payments. You’ll get there, I am proof of that.