Lifespan of electrons Me and my friend (we are both highschoolers) were talking about the fascinating field of physics and our discussion (initially it was about the something from this video 
turned to protons and electrons and their lifespan. I said that it was higher than the current age of the universe and then he said electrons age is more than the proton's. So when I came home I searched about it and find that though he was wrong as per the following :

[Source: Wikipedia]
but it led me to this article and here on stack exchange to this answer where the answerer states that electrons cannot decay further as this would lead to violation of the law of conservation of charge (as far as I can understand from it). So my question is: 


*

*What does it mean when we say about the lifespan of an electron?

*How is the lower bound found? 
 A: 
where the answerer states that electrons cannot decay further as this would lead to violation of the law of conservation of charge (as far as I can understand from it).

This answer is correct assuming that the standard model of particle physics will not undergo great changes from new data. There are speculative theories which try to find an underlying layer from which the standard model particles emerge. In these models it could  be possible to decay to ligher charged paraticles than the ones we have established experimentally up to now. BUT there is no experimental indication that these speculative theories could be correct, and some theoretical arguments that make them improbable.

So my question is:
What does it mean when we say about the lifespan of an electron?

Note the $>$ sign. It says that our experiments have determined no electron decays, and they can give a limit for the lifetime, i.e. it must be higher than the limit given in the table in order not to have been detected.

How is the lower bound found?

For the proton, which we know has constituents (quarks) and there are theoretical arguments that it could decay, special experiments are running, looking for proton decay, and that is why the limit is larger.
For electrons it is calculated from existing data, and there is a  running experiment here.
