Making bitcoin a retirement plan is profitable and i think it is the most secured way of making a retirement plan since it will be in your custody where you will have access to it at any time you want. 20 years is a very long time, by then the investment must have yielded heavy growth added with the quantity you have been able to hold. Inflation has worsen the fiat currency to an extent that it doesn't have any future value. Instead of saving money in the bank as retirement plan, bitcoin will be the most preferable way of investing that money. 20 years is about 5 cycles of bitcoin, and of course the growth of your investment within that interval will surely be huge.
It can be very profitable to buy and hold bitcoin for retirement plans, but I won't do that alone. I like situations where I diversify and invest in many more things, like also putting some money into real estate and other physical assets which can be yielding profit on a regular basis while you hold your bitcoin and wait for as long as you want until it gives you that breath taken profit you have been aiming for.
