Sylvinho was like 27 when we signed him.
That's one underwhelming list of players to be honest. Edu is the only one who ever turned into anything useful during his time here. The rest of them either stalled in their development or spent years abroad and never got the chance here. Vela started to develop again once he was out of Wenger's reach. I can see Ray's point.
On one hand I mostly think the track record is poor because there isn't a huge sample size. Then again, there isn't a huge sample size because Wenger doesn't favour working with young South American talent. There used to be valid reasons to not gamble on them, such as the difficulty in obtaining work permits, but that excuse has been out the window for a while now. We both could and should go after players like Gabriel Jesus and Gabigol.