The M96 motors do NOT have a life expectancy. There has been allot written about the various oil leaks and occasional failures of these motors, but only Porsche has the dealership data. I will refer you Excellence magazine, which has done an article on the M96 motor. There are thousands of examples that have many more miles on them. The M96 has been raced very successfully in the U.S. and in Europe, winning multiple races and championships. Now comes the part of the response where I give an anecdotal example to prove my point.
You also need to consider that a replacement M96 motor is about the same price as an engine rebuild. There are shops that will rebuild M96 motors now that they have been around for a long time.
This example is not a high milage car by any means.
It makes sense to buy the best 996 that fits in your budget. The condition and maintenance history of the car matter more than the milage.