You are correct. Updated.
Challenge Rating: 1?
Advancement: 3-10 HD (Medium); 11-20 HD (Large)?
Skleros stand 5 to 6 feet tall and weigh x pounds.
Isn't the second sentence of the martial training description unnecessarily wordy? Saying "Skleros possess the base attack bonus and feats of a fighter with a level equal to their Hit Dice" has the same meaning and is a lot more pithy than "Skleros possess the base attack bonus of a fighter of their level, and qualify for feats as if they were fighters of a level equal to their Hit Dice."
Also, should we give them a ranged weapon. Perhaps javelins?
Challenge Rating 1 seems OK, they're only a little tougher than a 2nd level warrior.
I was thinking they'd remain the same size, but just become more skilled fighters, so would prefer 3-10 (Medium) and add a note that larger varieties exist (e.g. a Large-size Ogre Skelos with 4-12 HD and a Huge size Giant Skelos with 8-16 HD.)
Well they ought to be lightweight, being naught but bone - 50 pounds?
They look pretty good, though one could quibble that ogres don't have 11HD. I'm happy with the advancement, but I wouldn't object to changing it to something like 3-6HD (Medium), 7-12HD (Large), 13-20HD (Huge) if Cleon really wants that.