It took me awhile, but I finally compiled a data set that tracks the average 401(k) by age for American workers from age 25 through 67. It was difficult to get a full apples-to-apples comparison because some studies use premises like “assuming two years of employment with a job before calculating” and also the data sources rely on averages rather than medians which has the affect of an upward skew because people with millions of dollars in a 401(k) raise the numbers of what is “typical.”
My view is that it looks like a good chunk of Americans waste the opportunity in their late 30s to sock aside a meaningful amount for retirement. By age 35, the average American has a little over $32,000 in a 401(k). But over the next four years, the amount only goes up to $39,000. Without factoring in any capital appreciation, that suggests a monthly savings rate in the realm of $140-$150. Because we don’t know the investment gains for the typical investor between those ages, we can at least establish that this is the upper boundary.