It won't hurt your average age as it will continue to stay on your report for 10 years, but if you don't have another installment loan open it may hurt your credit mix category. You could lose up to 20 points if that is your one and only installment loan.
That said, as long as you aren't applying for a major loan in the near future - make the right financial decision over the right FICO decision.
If you need your score as high as possible then pay down most of the loan to reduce the amount of interest you will pay and stretch it out until you have obtained the loan you need.
Goodluck!
