I know there are some countries that have different rules for some things that have been in your possession for more then 5 years for tax accounting.
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There are also examples where you don't have to pay anything at all if you can prove that you came into possession of the cryptocurrency before a certain date. Let's say that I have some cryptocurrency that was acquired before 2016 and I can prove it, I wouldn't have to pay any tax - although I don't have to pay it even if I buy and keep crypto-currencies for more than 2 years.
Considering the few posts that the OP wrote, it seems to me that he has other plans, although I'm not sure that he knows exactly what he wants.
That is the fun of taxes, depending on what country you are in, it can greatly change what you pay.
Since the OP has not come back to discuss all we can do is make assumptions.
Could also want them to prove they were in BTC that many years ago for some kind of scam, but there are other ways to do that.
-Dave
