I know about a handful of taken cared of (but driven spiritedly, once in a while on track) stock to stage IIIish cars with more than 200k mi on the clock. Come of the fastest stock turboed Zs I know of have 100kish mi on them.
Mileage has nothing to do with it. Maintainance and care does. If you find a clean one, have it checked out by someone who knows. If it feels strong and checks out okay, it probably is as good as new when it comes to turbos.