Automakers reported a nearly 12 percent gain in U.S. sales in January, a surprisingly strong showing. Higher used-car prices and the rising age of vehicles on the road boosted new-car sales. The average vehicle on U.S. roads is almost 11 years old-a record-and owners are now trading in older vehicles they kept during the economic downturn. Last month’s sales are the highest they’ve been since the 2009 “Cash for Clunkers” Program. The fact that this increase in sales has been accomplished without resorting to profit-sapping discounts is a strong signal that demand for new vehicles is finally returning to pre-recession levels. U.S. light-vehicle sales accelerated to a 14.2 million seasonally adjusted annualized rate in January, the highest since the August 2009 government trade-in program.