U.S. auto sales grew 6 percent in 2014 to 16.5 million vehicles, the fifth straight year of gains following the Great Recession, and with the upward trend expected to continue this year, San Joaquin County auto dealers are optimistic about their prospects. Helping set the stage are an aging national fleet - many consumers kept their cars longer or sought used vehicles during the long downturn - that now averages over 11 years old.