Will overclocking my cpu take time of it\'s lifespan?

more than 2 years

Every CPU is different.

Could last 5 years, could last 1 year. Even a cpu at default clocks might only last 1 or 2 years (unlikely) depending on how far and how often it is under stress. If the temperature is kept at an acceptable level it will probably last as long as it would if it were at default clocks.

As long as you keep the processor cool under load and the voltage under AMD's maximum recommended (approx. 60° and 1.4v), you will not significantly reduce your processors life span compared to stock.

Am I right in thinking though that by REDUCING stock voltage and using an after market cooler (keeping the temperature cooler than stock even when overclocked) you could increase the lifespan of the processor despite an overclock?

Also it maybe worth mentioning the average lifespan of a typical CPU.. I mean, shaving 2-5 years off of a 30 year CPU is a no-brainer really  
((I've googled around but haven't found an answer.. I've never had a CPU fail on me despite some massive overclocking of older chips))