Cute little guy! I love his color, to me he looks a little goose-rump-ish. And maybe his front pasterns look a bit weird, but maybe that's just the photo It would be easier if there were more pictures. Other then that he is a pretty boy!
Head is of good length (not to large or long) Good expression and nice big soft eye. Pretty small ears. Throat latch is a little too wide. Length of neck is good but is wide. Neck is set properly on top of chest which is good. Can't see his shoulder angle but suspect it is too straight as are his pasturns (these 2 angles always match) Top line is okay but needs muscle and condition. Croup is slanted and weak (gooserumped) Low tail set. Hip is a little small. Balance is uneven as his front half is bigger then his back half. (typical problem in miniatures) Under line is good but could be better with muscling and conditioning.
I hope you don't mind if I give you some show tips. I would undercut or thin the mane to lay flat. Also clip a little further back on the bridle path to showcase the length of neck.
When showing him take 2 steps back away from him. You are way too close :) He can't really show off if you are right on top of him. Because he has a weak croup you really want to set it and flatten it a bit. (its the handlers job to know their horses weakness and try to make it look better) He would show better just a bit stretched. For example one back leg stretched a bit.
Also working him and getting muscle on him should be a priority. Especially if he is over a year old
Goose rumped simply means a slanted downhill croup with a low tail set. A croup slanted down like that is not as desirable in miniatures as a tight flat croup. And a higher tail set is also more desirable. If you flatten that croup when you set him for halter it will look better. That pic above is still not really right. Since both back legs are stretched and his front are too far up he looks like a rocking horse. You want the 2 front legs planted right under them and just a little stretch in the back. I will see if I can dig up a picture here to show you.
Since he's 6 the judge is definitely going to want to see more muscle and conditon on a mature horse. You need to get some weight/muscle up on the topline and get that belly tucked up. Trotting up and down hill fixes that really well.