Maverik - From your second link
"Another reason for castration is to reduce masculine conformational features. Testosterone affects growth leading to earlier closure of growth plates in developing bones. The result is a shorter, stockier, more muscular stature. The muscles of the face, jaws, and neck are particularly powerful in the stallion. Castrating at an earlier age will reduce these masculinizing effects of testosterone. Unfortunately studies have not been performed in the horse to pinpoint the critical ages of testosterone’s effect on conformation. Likely it is sometime before 18 months of age since so much growth occurs by this age in the horse. "
This is what I said in my earlier posts. Of course, based on this article this becomes a moot point after 18 months of age as most of the growth has already occurred. So there would be absolutely no reason (height or muscularity) not to geld a horse (unless you were planning on using him for breeding) after this point. I