In your opinion how many Bitcoins would someone need today in order to retire by August 03 2019 or Aug 03 2020?
How old are you? Male/female? Any congenital diseases? Smoker/non-smoker?
Any children? Plan to have children? Have any fiat savings?
Anyway, assume 500,000 $usd per BTC by 2020 and do the math yourself. Less than 0.1 BTC per year * number of years you expect to live.