Well, yeah - there's always a tendency to overestimate domestic players, just like we see with MLS fans on bigsoccer. But a 19 y.o. being dominant in any league is pretty notable, and Argentina is not a weak league.
Why don't you comment on it yourself? davide is correct in saying that players under 17 (at least in England) don't have professional contracts. IIRC, Rooney played his first game while he was on trainee/amateur contract.