The Office of Personnel Management on Thursday released the final rules for a much-anticipated “phased retirement” program for federal workers, saying agencies can begin processing applications in November.

The move comes more than two years after Congress passed a law approving the option, which allows federal employees to work part-time while collecting half of their annuity rate after reaching retirement eligibility. Participants will have to spend at least 20 percent of their time mentoring younger employees, particularly those who will take over their former roles.

“Phased Retirement provides a new tool that allows managers to better provide unique mentoring opportunities for employees while increasing access to the decades of institutional knowledge and experience that retirees can provide,” OPM Director Katherine Archuleta said during a news conference Thursday.

Civil Service Retirement System employees will be eligible for the program once they reach age 55 or older with at least 30 years of service, or age 60 or older with 20 years of service. Federal Employees Retirement System personnel will be eligible after 30 years of service or once they reach the minimum retirement age, or at age 60 or older with 20 years of service.

OPM said agencies will have the authority to work out other details, such as deciding how many employees should participate and for how long, as well as how mentoring should work and be measured.

“Agencies have a lot of discretion in how they implement this,” said OPM human-resources official Mark Reinhold.

The federal workforce, with hundreds of thousands of employees considering retirement, has expressed lots of enthusiasm about phased retirement, but the plans became stuck in bureaucratic limbo after Congress approved the program in 2012.

Joseph Beaudoin, president of the National Active and Retired Federal Employees Association, said in a statement on Thursday that his organization received calls “almost daily” from public employees asking when they would be able to participate in the program.

“The new regulations are arriving just as the federal government faces a critical retirement wave,” Beaudoin said, noting that the number of retirement-eligible federal workers is expected to double within the next three years. “The phased retirement program should help stem the tide of this retirement surge.”

Rep. Elijah Cummings, a longtime proponent of phased retirement, applauded OPM’s release of the regulations on Thursday. “I expect that phased retirement will be an invaluable tool for agencies to ensure the preservation of institutional knowledge and the readiness of a new generation of skilled workers as the baby boomers become eligible for retirement,” he said in a statement.

The nonpartisan Congressional Budget Office estimated in a May 2012 report that the phased-retirement program would save money, decreasing direct spending by $427 million over the 2013-2022 period as participants draw a lower retirement benefit than they would receive through full retirement.