Lets say I want to buy bitcoins today and store them for 20 years to use a my retirement fund. Live comfortably, but don't need to buy a yacht or anything. How many do you think I would need to buy?
We don't know what will happen 20 years from now, maybe bitcoin will not survive to that date or maybe bitcoin will survive but the price is unpredictable because its characteristic of not being stable and that's the one reason why bitcoin is unique. So while you're still alive just don't be outdated of the news related to bitcoin. So you can control your coins anytime.
it is always have to side possibility , became worthy or became worth nothing ,
noone can guarantee bitcoin will keep growing and survive for years even satoshi the inventor ,
so don't go allin in this awesom bitcoin world , but keep your faith in bitcoin ,
i myself planning to hold 10 bitcoin atleast as future investment.
I think bitcoin is not going anywhere at least for next 10 years but not sure what will happen in future, so I will never hold my coins for next 20 years but will sell when I am satisfied with the price.