It's possible to permanently strain your voice, however that doesn't appear to be the case with Trent. His voice is just progressively changing with age, which usually results in a deeper voice. You can really tell in comparing his speaking voice now compared to older interviews and what not. But this means that higher notes and the piercing screams he used to do aren't quite where they used to be in relation to his current vocal range.
I don't think I've ever heard Trent sound like he really strained his voice to the point it affected his singing, which is surprising, since he's always gone pretty much balls out in any of the shows I've seen or listened to, especially the older ones where he did a lot more screaming. Case in point, I was just listening to that Stanhope Lolla show that @
RITCNIN posted and that's a VERY aggressive show, but his vocals hold up the whole time.