You've probably heard of the FIRE — financial independence, retire early — movement, the trend that's taken hold among individuals who are mostly in their 20s and 30s.

But you probably haven't heard of the "super savers," Americans age 45 and older who are putting away at least 20 percent of their income — or $1 out of every $5.

A new online survey from TD Ameritrade of 1,503 individuals in September and October found that 20 percent count as savings over achievers.

"Most are choosing this path because they're looking at the freedom and flexibility it offers," said Dara Luber, senior manager of retirement at TD Ameritrade. "They are looking for financial security and peace of mind, and they're thinking that their retirement will be like a second childhood."

The survey found that 57 percent of super savers plan to retire earlier than their parents did, versus 46 percent of non-savers.