Stock speed is 3.2 so it shouldn't be at 3.0 or 3.1. If you are looking at the speed in task manager, there's your problem. That is not reliable. Use cpuz. Turbo speed also depends on how many cores are being used:
3.2 GHz (4 cores)
3.3 GHz (3 cores)
3.4 GHz (1 or 2 cores)
It will not shorten the lifespan and actually all desktops will run turbo all the time if needed since you do not run into power or heat issues on desktops (normally). And no you can't oc. Please don't give wrong info.