The short answer is no one knows. Unless you can time travel, maybe. As the old saying goes—predictions are hard, especially about the future. In short, it’s a cryptocurrency—the phrase “crypto” is a reference to cryptography, which is part of the technology that underpins the system. This digital currency has value in part because some people accept it as a form of payment, in part because it is scarce (there is a limited supply), and in part because you can exchange Bitcoin you own for dollars through an exchange like Coinbase.
Bitcoin is highly volatile, and is thus not a conservative way to build something as essential as retirement. Bitcoin and other cryptocurrencies are so new that the market is still essentially trying to figure out their value. We don’t know what it’ll be like next week, never mind when you near retirement age.