Overclocking will only shorten the life of a CPU if you let it get/stay really hot, (like 70-80 c) or increase the volts to idiotic levels (which will make it run really hot)
The CPU in this system stays around 45-50 C during heavy gaming, and considerably less at idle. I only slightly increased the volts so this CPU shouldn't see any significant shortening of lifespan. It only really has to last 2-3 years anyway before it will need to be replaced due to being ancient technology.