Credit scoring is hardly a perfect science but an art. Age of trades is one variable, the others are delinquency (which has the largest effect on score), number of trades and utilization. So if use a card, even as a transactor that has a low line, but on the day the credit is pulled for scoring your utilization is high relative to the credit line that can also lower the score. Mortgage and auto loan rates will be priced according to score, but in fairly large score bands so a 10 point difference may not be that great unless you cross a score band.