IDK. Really depends on your precise path. My spouse and I are about 40 and, barring some truly collapse-type scenarios, our retirement is pretty much assured. We could make no other contribution and just let what we already have grow, and it would easily cover a very comfortable retirement at age 65. At this point further contributions are about moving that date forward.

We did it through being DINKS, both with engineering careers, general frugality, and getting on the property ladder pretty early. But it was a combination of luck, skill, hard work, good decision making, and luck.