DS10, who has some math talent, noticeably lagged in geometric concepts that depended on visual spatial ability at around age 6-7. It stood out because he was able to assimilate elementary mathematics without teaching/curriculum sufficiently that he was able to do well through 5th grade end-of-year math test for his first math acceleration to compacted 3rd/4th grade math in 2nd grade(age 7). At that same age, he was also able to grasp basic algebra conepts instinctively. The geometry lag really stood out altough he did not have quite the extreme difficulties evident with your DS. He could discern geometric patterns and area/volume problems were easy, etc. However, I did notice enough to sit down and spent a little bit of time walking him through some of the visual spatial stuff (flip, turn, rotate). Interestingly, his twin sister, who is not talented in math, really excelled with the geometry stuff, probably because she is very artistic.
In DS' case, the visual spatial issue was one of the reasons that I pulled him back and did not accelerate him beyond pre-algebra for 4th grade. Interestingly, by 4th grade (age 9), he had matured enough to excel in the geometry units in his pre-algebra course. At this point, I am not concerned with his ability to handle a geometry course.
I wasn't super surprised by his relative weakness with the visual spatial aspect of geometry around age 6-7 because he still had letter reversal issues at that age even though he was reading Harry Potter level books fluently. He was and still is (although not as bad) very bad at judging size/distance. His handwriting is still awful, including poor spacing. I think part of it is maturity and part of it as learning to compensate.
I would keep an eye on this issue for sure. The inability to discern patterns is the most concerning. You can work with him in pointing out subtle differences and see if he catches on. There is also a big difference between an inability to grasp the concept of angle (cognitive issue) versus the inability to accurate measure an angle (fine motor/visual issue) or the inability to scan/judge angle size (visual spatial issue).
