Your horse drops his head nicely and looks as if he is using his butt nicely. Since it's such a smaller sized jump I wouldn't expect to see much roundness through his back so that's okay. He also rolls his shoulders over the peak of the jump where as they should be lifting his knees towards his face, not tucking them under his body, nothing some gymnastics or bounces won't fix. He is probably just green and hasn't quite learned how to snap his knees up more, which is important if you guys would like to move up in jumping.
Your jump position looks very balanced. The release looks a little iffy, kind of like you couldn't decide between a crest or auto release, but it isn't holding him back which would be a bigger problem. With a younger horse I would suggest a crest release to start out with until he really knows his striding and what to do if you chip so that you can always have mane to grab onto if needed. You turn out your knees when you get into jump position which makes you pinch with your calves. Try some no stirrup work and making sure you have even contact throughout your thigh knee and calf so you don't end up holding on by your calves. It'd also be easier to turn your knee back in if you could sink into your stirrups a little more. Other than that You both look wonderful and best of luck!!
The above poster really nailed everything perfectly :)
My advice would be to shorten your stirrups a couple holes. It seems like you are almost still in the saddle, and your leg is long. Over these jumps, you probably don't NEED the shorter stirrup, but it will definitely help stabilize you a bit more and get you off his back a tad. I love your release. Your toes are pointed out a bit, but I know how hard that is to correct. Just keep working at holding with your whole leg, not isolating your knee of calf, and you'll be good as gold! :)