Yep, if you're serious about saving, this is entirely doable. I'm not at all on track for this because I'm not dedicated enough. But when I lived and worked in the bay, I knew a couple of guys who saved >50% of their take-home every year. They maxed out their 401Ks in the first few months and then redirected the money to other savings. Someone earning $100K before taxes can absolutely save a million in cash by saving aggressively for a decade and a half.

Hell, my roommate in grad school earned $30K/year and managed to save $10K one year, despite buying a (used) car. This was the result of cheap cost of living and generally just being really frugal.