Is there any financial product that would allow someone to invest a sum X (once or maybe add funds periodically) in a single stock, an ETF or similar for a minimum period of time, say 100 years?
I'm aware that there are products like "fixed deposit", which guarantee a specific ROI on the long-term investment (usually no more than a few years?), but the question is not about a predefined ROI.
For example, if someone wanted to invest money in the stock market for their (yet to be born) great-grandchildren, is there a way to ensure the money stays invested until a substantial increase in value has happened hopefully, and to prevent intermediate generations from selling earlier?