You need about 3.5~5 mln dollars to retire at age 30.
So that makes it about 30.000~40.000 btc.
Since i can't see bitcoin skyrocket any time soon i think you need a lot more though.
I bet on 1000 U$ / BTC before 2016, so with 8000 BTC converted to fiat, it returns 8M, give 4M in taxes, 4M left, that should give 100k U$ / year. If we take in account how much hyperinflation we may see in the next decade, we're fucked up. So, better stick on BTC and wait for the day you'll be able to retire all-in BTC... imho, within 10 years..