I hate to split hairs, but you'll take home about $80k on a $120k salary, so the plan you've proposed would require over eight years of slumming it, not five.
More on topic, imagine that you try to retire with $500k in the bank at 35. Even if you're willing to slum it at $20k/year for the rest of your life, you'll only make it to 60! And that's ignoring the elephant in the room, inflation. With mandatory health insurance, $20k/year's going to be tough to clear too. You're probably going to have to seek disability status to qualify for government assistance at some point if you are fixed on the "early retirement" goal.
Now, it's not like you're going to throw the $500k in a mattress. Surely some combination of bonds, index funds and specie can spare you from the worst of outcomes. I don't know about you, but all of this sounds like a mean and tentative existence to me, babysitting a nest egg. There's not much wiggle-room for taking risks, like starting a business that's more interesting than "freelance programmer."
In summary, I doubt that one can retire early with any comfort off of a decade of decent earnings. That's not really controversial, but it disagrees with your financial advice, which I suspect is dangerous. I think it's a bit irresponsible to suggest that somebody spend the prime of their life squeezing out every last penny. I think it's unrealistic to suggest that the difference in rent between a convenient walking commute and a safe, 10-mile bicycling commute can equal the budgeting difference you've proposed. Lastly, you're ignoring the opportunity cost of living like a monk when it comes to professional networking, or more important things like having a varied and healthy social life.