I have a 16.3hh horse and i got her when i was 14! She was strong, and a pain in the butt, and a bucker, and straight off the track... but she taught me to never give up and to face life straight on with all you got. Shes my heart horse even though she gave me 3 concussions, she also gave me a winning round in jumpers and hunters and intro dressage test C. dont go off getting hurt or anything 😂 but if you love this equine as much as i love pride, go for it, and it will be worth your time and effort in the end
No problem with the size. You only need to be able to stay on his back whenever he moves and to control him, just like any horse. The only problem you might have to face, is the little length of your legs : if you want to do lots of dressage, he will need some time to adapt, but it should be quite quick (1 week maximum).
It is okay even if he is strong, as long as you can handle it! The only reason why it may be an issue is that a tall horse has bigger stride and it is not always comfortable for shorter rider to sit on it (due to that your legs are not that long, when you sit on a bigger horse it is harder to keep your balance).