It all comes to discipline.

If you are always thinking of you're holdings, you will feel that 3 months = 3 years. If you always think of the possible profits that you can get in holding Bitcoin, you will feel that 5 days = 5 years. You get my point. I guess the owner of that address just forgot that he got that amount of Bitcoins, and I don't know if we can consider him as lucky because he still got the private keys after more than a decade, or he really kept the keys for a reason.

How long can I hold? 5 years is the minimum, but I can still hold it even longer when needed. I mean I know that past performance doesn't mean it will happen in the future, but I believe it will and if that happens, all Bitcoin holders will be happy.