At the end of the day it's your choice, but believe me no one would suggest keeping rocks, they are unsafe even if they are big (google axolotl impacted X-rays) and as I can see from your pic it harbors food and gunk in little cracks that can be a massive pain to clean properly and can miss spots (I used to miss spots when I thought I did a very thorough clean!)
I used to have large stones too like yours before and I witnessed my axolotl suck one up completely but thankfully she spat it out and that pretty much convinced me to change.
I am unsure about mating rituals but you're right with the age thing.. If raven is a girl and under 1.5 years or under a certain length it's very stressful for her to mate. I know boys occassionaly wriggle/shake around when they want to mate, does he do that?