As a recent college grad, I have a very positive net worth (given my age and having just started out), yet due to my age and income, I am an UAW. I'd say the MND rule of thumb probably isn't very accurate if you went to college and are under 30. But assuming by the time you're 30, making $50,000, it shouldn't be too hard to accumulate the "average" amount of 30*50000/10 = $150,000.
In a more extreme example, an MD just getting out of med school and interning/residency would be making big bucks, but would likely have a negative/low net worth, so they may not even be able to use the general guideline till age 40!