Cordero is 21, but he's small and that goes against him... 1'75 I think.
Montero is one of the worst defenders in International: if he wasn't, he would be the first option by far. That's why Hourcade is apparently working like a beast to make him into a decent tackler at least. Watch out the first try of SA against us in TRC this year.
Agree entirely with Horacito on his view on Montero - I heard that it is a matter of maturity, although I believe that he will come out very well!