Thank you... I do think we learn slower as we age, but that's only because we get out of the habit of learning. The more we do the better we get.
I must revisit French at some point; I was put off it years ago by some Parisians scorning my accent, which is silly really, as I wasn't learning it for them.
Funnily enough, from the little I know about French, I actually think Mandarin could be a good learning partner. The way they do their numbers is very similar to the French, so I wouldn't be surprised if there were other similarities, yet the vocab is different enough not to get confused.
Yes we will stay sharp into our old age, it will be many many years before the blockchain sees the back of us! :-)