Rather than giving them direct advice about bitcoin, teach them the concept of it. What it does and what it is capable to do in the future. We are the one who should guide the next generation to the right path. And I don't think there would be any issue teaching a 10 years old kid. I know Bitcoin knowledge is complicated if you dive deep into it, but when it comes to basic knowledge, it is not that hard to understand or to teach a 10y/o kid. Also as they say, practice makes you perfect. If you start from a very young age, you can learn it and keep learning to master it for a long time. Thus becoming the best. But no one should force a kid to do so.

And when it comes to elderly. I think it is very complicated. If they already have some knowledge on something that is similar to bitcoin, then it's just an update for them. You just need the right approach to do it.
And if they are not interested in it. Then it is better to leave it that way.