A new study estimating that just 12 percent of low-income older Americans save in a 401(k) or similar employer retirement plan also suggests that many more would save – if only they could. The researchers – April Yanyuan Wu, Matt Rutledge, and Jacob Penglase of the Center for Retirement Research – focused on individuals between ages 50 and 58 with household incomes below three times the poverty line. That was less than $36,357 in 2010 for a one-person household, for example, and less than $46,800 for two people. The period studied spans 1992 through 2010. Retirement saving primarily takes place in workplace plans. But to participate in a plan, workers must clear four hurdles. First, they need a job. Next,…