The Length of History on your open and active accounts affects 15% of your FICO Score. Basically, the older an open and active account is, the more points that specific account will be worth towards your credit score. On the other hand, new accounts can reduce your credit score because of their lack of history. In fact, if you were to go out and buy a new car, open a credit card or even refinance an existing loan, you will see your credit score drop when that new account shows up on your credit report. That is why your banker might advise you to avoid opening accounts while refinancing your mortgage. Did you know that the average person has at least one account that is 12 year old or older? People with 760+ credit score have at least one account that has been open and active for 19 years on average. Since the FICO score system only gives you points based on your open and active accounts, your credit score is basically as old as your oldest account. A better way to explain it is this: if your oldest open and active account is only 6 months old, your FICO score is only taking into consideration 6 months worth of credit history. It doesn't matter if you are 50 years old. If your oldest open and active account is only 6 months old, then your credit scores will reflect that.
Another interesting note regarding the length of history on your open and active accounts: it is in your best interest to keep a hand full of credit cards open for the rest of your life. The longer they are left open, the older they get, the more points they are worth. Credit cards or revolving accounts are the only types of accounts you can keep open for as long as you want. Installment loans such as mortgages, auto loans, student loan etc. will close once they are paid off. You'll never be able to establish too much of a credit history on a car loan because those types of loans typically only last 3-6 years. Once that car is paid off, the account closes and you can say bye bye to all the credit score points that you earned while paying your car on time. Even a mortgage will be paid off or refinanced at some point. Installment loans are temporary. Once they are paid off, they're gone. It's best to establish about 5-7 revolving accounts and keep them open forever, never close them out. Maybe open a few extra just in case you don't like the terms on one of them or perhaps one of the companies backing the credit card goes out of business (all too common now day).
Thanks for reading how the FICO Scoring system considers the Length of History.