If you want to live comfortably in retirement, bitcoins are the wrong place to look. Check the history. They've been going down in value all year!
Invest in FacebookCoin or whatever it's going to be called, or maybe just invest in a low cost index fund (since you're talking 20 years down the road).
Umm, check the history? perhaps you can go back more than a few months? I think the overall return on Bitcoin has been pretty good. from a few cents to over $400 in a few year years? Has any investment in our lifetime been that good?
Facebookcoin? Really? You would trust hard earned money in an account with the kind of "security" Facebook is known for?

if you want to retire in 20 years you need to have allot of bitcoins how many money do you want 1 million you need atlest 1400 bitcoins for now.