Can't buy my lv20 racial mount

Im playing at onyxia as a lv 26 paladin dwarf and when i go to the riding intructor in the dwarven area the aprentice riding skill doesn't appear in the instructor's tab so i can't buy it, and the lv 20 rams also doesn't apear in the ram merchant, please help

I believe you can buy your first mount at level 40 at the moment (vanilla content) on Onyxia