Average lifespan

I think that would be a difficult question for anyone to answer. From my experience, my Deathadder 2013 mouse wheel button stopped working and I barely used it, and my Blackwidow Ultimate 2013 Battlefield 4 has plastic that is discoloured and slowly disintegrating (I thought it was dirty, and I scratched it, but I scratched a little plastic off). It is 5.5 years old though, but I still don't think it should happen, as it's never in the sun.

Yeah, there isn't an universal answer. I am still using Megalodon that is about 7 years old. It works perfectly! But I also had an Imperator about 5 years ago, on which rubber started to peel off after just 2 weeks of use...

i think it really depends on how you use it..