In 1964, Irwin Lipkin became one of the first employees at a small New York trading firm called Bernard L. Madoff Investment Securities. Five decades later, Lipkin, 77, is set to be sentenced on Wednesday in Manhattan federal court for falsifying records, marking the end of the criminal case stemming from the collapse of Madoff’s multibillion-dollar Ponzi scheme more than six years ago. Madoff, 77, who is serving a 150-year sentence after pleading guilty in 2009 to masterminding the fraud, has always insisted he acted alone.