I see this question all the time:
"I just got this baby pony/2 year old pony/3 year old pony and I'm not sure when I can start it's driving training. How young is too young to start training?"
If I comment on the question I will typically say I start their training right away. They learn to have their feet handled, they learn to lead, they learn to follow me, walk beside me, walk in front of me, they learn to stand tied quietly, they learn to go for walks and hikes, they get ponied behind the cart, they get trailered places in the horse trailer, they learn when they can eat the grass and when they can't...
There are so many things one can do with a baby or a young pony. It always catches me by surprise when people think they need to start putting the harness on their young pony (or even that they need a harness to figure out if their older pony will like driving.) Start simple!! Start with a halter and a lead rope. Teach them to walk behind, then beside, then in front of you. You can do this with just one lead rope.
When I used to train professionally there were times when I had a pony come to me that wasn't even halter broke. You could put a halter on it and sometimes it would go with you, but it didn't actually understand pressure and release, following a feel or seeking comfort in the neutral. These same ponies were difficult to brush, handle their feet and basically be around them. It's surprising how many ponies make it to adult hood with very little as far as manners go. Why not start when they are young!?
I wish I had someone to follow me on all our walks. It's so hard to communicate just what it is that I do with my ponies.
We walk, A LOT! I have one pony on the right side of me and one pony on the left side. Then when we turn around I have them switch sides. This ensures they don't get 'one-sided' or comfortable being led on one side more than the other.
Sometimes I ask them to walk behind me. Sometimes I ask them to walk beside me. Sometimes I ask them to walk in front of me. I rarely have two long lines. I usually only have one 10' lead rope on each pony.
Oliver is learning that the word "walk" means to walk. Soon he will learn that "trot" means to trot! And when we are doing more ponying behind the cart he will learn that "canter" means canter as well. It's amazing how quickly they pick up on this when the other pony already knows the commands.
Oliver is learning that when the 10' long lead rope gets tangled around his feet, it's not a big deal. I will save him if he just waits. He is learning that if he steps on the rope, he should just stand quietly until I help him. He is learning to walk along with the rope between his front legs, sometimes between his hind legs. He is learning to have the rope draped all over his body, his neck, his withers, his back and his butt. He is learning if the rope loops around behind his hiney he should come around and line up beside me.
Oliver is learning about mud puddles and sticky, slippery mud. He is learning about climbing hills and then coming back down them. He is learning about walking through sage bushes and soon he will learn about crossing creeks and bridges out on the trail.
He is also learning about wearing hoof boots and being mannerly when I put those on him.
These are things they can learn and then learn more about and then perfect. Some of these things Zorro is STILL perfecting. lol!
So when do I start their 'real' driving training? I wait until they are 4. Then they start the ground work with the travois, the bit and the harness. But until then there is more than enough we can do!