Truth be told, I have never been a millionaire, so I can't give advice to one, young or old. None of the people here are millionaires neither, unless proven otherwise, so getting advice from people who have never experienced this, will not be a good advice at all. I think the best thing we could talk about here would be just what we are lacking and what a millionaire may not lack.
Yes, that is the kind of advice which must come from someone who has already had access to millions of dollars, as he will have the experience to answer that question accurately. Most of us here, if not everyone, would also need such advices if we were in the shoes of the young hypothetical millionaire. We can imagine what we could do with a big sum of money, but it's just speculation.
The truth is that reality would be totally different and we would feel lost and unsure on what to do. Probably to seek for a professional financial advisor would be a good idea. Personally, I wouldn't trust random people on the internet regards what to do with millions of dollars... To invest in Bitcoin would be a certain thing to do, but not with the whole money disponible.