My situation may be somewhat unique, in that I've had grey hair since I was 18. Not a HUGE amount at 18, but... people noticed. By the time I was in my mid 20s, it was definitely noticeable - more pepper than salt still, but noticeable. By 30... there's a fair amount of grey showing. Early 30s I've got people thinking I look good for being in my late 40s (had that more than a couple times).
But when it came to interviewing and opportunities, I was already feeling the age stigma in my late 20s. "Not a cultural fit" - not even in silicon valley mind you.
Had someone interviewing me - early 30s - said "well your resume only goes back about 12 years or so, what were you doing before that?" "High school". "Whoah..." - later found out he's assumed I was mid 40s.
Could I dye my hair? Yeah, but.. it's a pain, and... other parts of me will get old too. Not worth it - want to get hired based on ability, etc.
What's sad is to hear about the mid 30s folks wanting to get plastic surgery to look younger, which just validates and perpetuates the continuous youth culture. May not be possible to fight it at the Facebooks and Googles of the world, but it shouldn't be this bad...