For years, insurers have charged older customers far more than younger ones, in part because of older residents' higher use of medical services. Now, as Congress wrestles with a healthcare overhaul aimed at covering the majority of the uninsured, that discrepancy is one area targeted for change. The outcome could affect tens of millions of people who don't get insurance through their jobs and buy it on their own, as well as some small businesses. It would not affect people who are covered by Medicare, or people who work for large companies, which usually get group rates for health coverage.