He suffered a massive decline in his late 20's and just wasn't the same player any more. The fact that he hit those numbers is more testament to how talented he was in the first place.
That was also part of my point. Even if Alex Teixeira decline after 3 years and some of his pace goes, quality players will be able to alter their game and still contribute.
Loads of players are still able to do produce without being dependent on pace.
If that applies to this player I dont know, but I dont think there is a window age wise that is set in stone.