Not the best question to ask but rather ask this question to their selves which is how much bitcoin can I save before I can think about retiring since it will all matter on your financial capabilities. Since if you have a lot of money then maybe you can buy a lot more. But if you have enough just to buy your basic needs maybe you will struggle to find the exact figure on what is the exact amount and when you can retire because accumulating is hard when we are not financially capable.