Horses are motivated by four things,
Reproduction - driven by nature
Not necessarily in that order.
They learn from repeated actions
Horses live in the weather and if you don't make an issue of it they won't either.
I lived in the high desert for years and we had wind 99.9 percent of the time and thunderstorms with lighting zapping from sky to ground. I would take my horse out in it all the time and she never had issues with it. When I moved to northern California I was boarding my horse and another boarder had asked me with a confused and shocked look if I was going to ride today. Winds were about 15 to 20 miles an hour. I said absolutely. This person said I was crazy. Maybe so, but I don't let rain, wind, thunderstorms stop me and my horse from enjoying life. The most beautiful time to ride is right after a fresh rain in my opinion. I've never ridden in snow, but I don't know that I would ride in a hail storm. Even horses will seek shelter from hail.
You have a long road to haul! This is not only a learning process for you're horse, but one for you too. As time moves on you will have learned many lessons and your horse will tooo.
One of the young horses I just purchased has an issue where she would swing her head at me and try and bite while I approached her when she's eating. She's getting better, but it will be awhile before she gets it in her brain that I'm the alpha. So every now and then when she doesn't expect it I go in take her halter in hand (when she swings her head I wack her one in the shoulder) and we go for a walk around the barn and back to the food. However, she has her own stall at night unlike your horse. The other young one I purchased tried that only one time. I took a hold of her halter (while I was telling her quit - I had to grab the halter quickly for I knew she was going to tell me to BACK-OFF) so I get the halter we walk away from the hay and the turned to face the hay. We stood there for a short period of time. I waited for her to say OK I want my food and when she made that first forceful move I pulled back on the halter and told her NO! And told her to stand (I don't think she knows what the word stand means) but I'm teaching her. When she settled down before she could make the move of I WANT MY FOOD I walked her to the hay and reached down with my hands and fluffed it up and she kept eating, but watched me. She learned the first time around. However, my other mare who is still learning the food game is taking longer. So it all depends on you being persistent with the same commands and actions and it depends on your horse as far as when he will decide to accept what you are teaching.
Now my 28 year old when she was 4 1/2, she was eating her dinner I was in the stall patting her on the girth, which no doubt pissed her off! I wasn't expecting it, but she turned around a bit me in the hip. I was all of 98 pounds at the time and she left nice pretty color bruise on my hip about 2 inches in diameter. I was shocked, but I knew I had to do something to get the point across that this is not acceptable, so I bit her back in the neck and scrambled from her stall. aaaaaaaaaaaa mouth full of dirt, but I got the point across. She was so stunned that I bit her back she stopped eating and just stared at me
Then when she got over her shock which lasted several seconds she went back to eating. She's gone now, and I do miss her, but I am so grateful that she and I became one. That was just one of many lessons I taught her and she taught me. Oh by the way she never once bit me after that incident which our time together was for 27 years.
PS an 8 or 9 year old in the horse world is considered a teenager, but they can be mentally immature (or what I would called not taught to interact with humans) horses will act like horses because that is who they are.