Do not feel safe about 5 bitcoins for retirement in 20 years.  Well if you are lucky you may have your guess of $100K of each bitcoin price.  But bitcoin price is volatile and you cannot predict how much it will gain or when it will go low.  If you want to be safe with your retirement, just earn as much as you can while you are able.  And do not rely only on bitcoins.  We do not hold the future.