Truck Payoff Question

Here is a little background to the situation. Sorry if its a little too long.

I bought a new truck a year and five months ago at 8.49% interest. I obviously didn't have good credit then but needed the truck for work. I paid the monthly note for the first year and built a 6 month emergency fund while getting enough in my 401K to get my full company match. The last 5 months I've taken strides to pay it off quickly. I now only owe 2,500 on it and saved thousands of dollars in interest over the life of the loan. I can pay off the loan in full right now without hurting my emergency fund.

Should I wait to pay off the last 2,500, break it up into small monthly payments or pay it off now? If I wait to pay it off, how long should I wait? I'm only curious because the only negative part of my credit score is the average age of credit lines. I'm worried if I pay it off now I might lose out.

Thanks for the information.