You can check which linux kernel version on rasberry pi a couple of ways, the easiest is using the uname command

BASH

uname -r

which should give you something like this (but probably not exactly this... hopefully)

If you wanted a bit more information, and not just the version you can run

BASH

uname -a

uname by its self does not give much useful info...

Yes my version is very old, i need a new one! :)