Aug. 4 (Bloomberg) — Chad Gentry would rather bet on his own ability to save for the next 40 years than on the U.S. Social Security Administration's solvency, so enrollment in his employer's 401(k) plan was a no-brainer.

"I wanted to take advantage of that to help build retirement from the start," said the 24-year-old, who has worked as an accountant at Fleet Feet Sports in Carrboro, North Carolina, for three years. "I've gone in with the mindset from day 1 to not plan on getting any Social Security."

Concern that the future of the federal safety net for seniors is precarious and the ubiquity of 401(k)s are prompting those born from 1979 to 1996 to get an earlier start on saving than prior generations, according to a report from the Transamerica Center for Retirement Studies. Millennial workers began building nest eggs at a median age of 22, younger than both Generation X, which started at 27, and the baby boomers, who started at 35.