Currently I'm writing a thesis in Computer Science for which I need to introduce and compare several open source tools that are available for performing a certain type of testing (mutation testing) on some piece of code.
To reduce the number of tools (initially more than 25), I set two limits :
The tool must have been updated in the last 5 years to be present in the list, otherwise it is considered obsolete.
Only tools that work for one of the 3 most used languages are considered. I defined them with the TIOBE index (Java, C/C++ are equivalent for the tools and Python).
I arbitrarily set the first condition to five years, but I would not be able to justify this number if needed. I didn't find a study or article with a point of view on the subject.
So my question is: After how many years without updates would such a software (or any software) be considered deprecated?