I only have a handful of documents that are about that age: my birth certificate and high-school graduation diploma.

Here's an interesting aspect of these: I did lose my college papers a while ago, and when I asked my college if they can produce a copy, they told me that they keep their records for just seven years. So, they had nothing. The high-school I went to doesn't exist anymore. So, if I had to recover my high-school-related papers, I'd have none. But, if I really had to, I could recover my birth certificate, as those don't seem to have an expiration date.

Anyways. In terms of storing digital copies, very little of that is relevant. Even ten years ago most authorities wouldn't be able to accept digital copies. Even today, the municipality of the city I live in won't take digital copies. There's no process through which I could have a digital copy they would recognize.

So, I need to keep hard copies. And the digital copies? -- well, they are perishable. I keep them for convenience, because every now and then I run into some situation where they are accepted. But losing them won't be a big deal as I can always make more of those. So, I don't need any exceptionally reliable storage requirement for the digital documents. It's more like a cache, which can be eventually retired.