Am I right if I say that once a Brazilian player goes the wrong side of 30 these days their services to the NT is no longer needed? It always seem like Brazil is bringing in new players, I guess they are one of few National teams that can actually be in a constant rebuild without affecting the player quality much.
Its not necessarily the case. Brazil do have a lot of young talent, and some of them get really early chances (18, 19). But some veteran players do stay on, like Lucio, Julio Cesar, Maicon and Elano right now. And it wouldn't be surprising to see those players feature in 2014.
It is a young NT, especially upfront right now, with Robinho being the oldest player in the starting front 4.
In Brazil the national team does have its own "rules", so to say. The coach won't pick the best 23 Brazilian players around the world at any given time, but rather those he's accustomed to, and that have played well for the NT in the past. That's why the 2010 WC team featured players completely past their best club days like Gilberto Silva, Kleberson, and especially Elano. Everyone can see that Elano's club career hasn't gone very far, but he's had a spot with the NT for the past 5 years now because he does well for the NT.
Personally I don't agree, I don't think you'll be beating top sides with midfielders who have proven they can't play at the top level of world football, but that is how it goes.
And finally there's the issue of getting completely burned. Mostly that's in the eyes of the media and the fans, but it will make a player a complete outcast. Examples are Felipe Melo and even Kaka right now. Felipe Melo is a decent midfielder, should get considered at times, but he's unlikely to ever play for the NT again because he got sent off in the WC QF. Kaka is still probably Brazil's best attacking player if fit, but he also can't book a spot in a 22 man squad. Granted, Kaka should be back in the future, but he's still a bit burned because of 2010. He played through injury to be at the WC, but because he was expected to deliver and couldn't, Brazilians judge him a poorer player than he really is.