I am sorry, but there is not such a thing as 'the more appropriate age for a kid to learn' or to show their inclination. There is no '
Human User's Manual (for Idiots or not!)' because every individual is
DIFFERENT from any other one. Period!
Personally, I did not (probably, 'refused to') speak before I was two years old; but, when I did I spoke flawlessly, like a grown man, because my family did never use any 'baby-talk' nonsense with me.
And, the moment I spoke, I also begun asking questions; lots of questions; and about anything new to me. I remember myself when I was three years old 'driving' our car with my hands on the wheel, while sitting on my father's knees and feeling car's wheel steering by itself, until I noticed that my father was also holding it at the bottom, out of my sight! If this was not encouragement and familiarisation, what else could it be?
Well, before I was four years old I already knew and easily recognised what a cold junction was, and clearly comprehended the benefits and the drawbacks of the in-series/-parallel battery topologies, already using my father's soldering iron and multimeter and assembling & playing with electronics kits, while dissecting anything I could lay my hand on! When I was five, I had my favourite Christmas present, a 1002 Circuits Box («?
?»: 'Polikiklomatistis' --I am sorry for the
unreadable characters-- was the name back then). It was a giant box with lots of various components with their leads terminated to exposed small springs, which could be interconnected by wire to form '1002' simple and complex circuits, providing also with instructions and literature). A year later I was struggling to understand what a resistor, a capacitor, a diode, a coil, a vacuum tube, a relay, etc. were, already having university literature in my hands.
So, expose your children to any possible field and let them ask questions. You will very soon see what their field(s) of interest will be; and do not forget to encourage them to get their hands dirty!
-George