As much as I love Bitcoin, its volatility can't be denied. If you don't have the time to ride the rollercoaster for a decade at least, I think it's reasonable advice to stay out of it or have a tiny position.

So if grandpa has just a few years left, and has a bunch of money he wants to spend on himself, I wouldn't advice him to buy Bitcoin.

On the other hand, if grandpa wants to leave a tip for his grandchildren... I think Bitcoin turns into a reasonable option again.

It all boils down to time preference I guess.