I guess "senior engineers" can be up to interpretation. Colloquially, I take it as someone with mid-career experience. For most of the FAANGs, "senior" can be reached in as little as 3 years out of college, with a median somewhere around 4-5. For a 30+ year career, one can safely assume your compensation will continue going up from your "senior" title 5 years in.

To summarize: yeah, I suppose $500K 4-5 years out of school isn't achievable, but within 10 it is.