I don't understand what happened there or how the guy who tried to overthrow the government is still walking free.
You know you don't understand what happened there, but you still assume he tried to overthrow the government. That's highly implausible. A much simpler explanation is that he wanted to quit on his own terms before it's too late, but needed the other party to start listening and, ideally, enter the negotiations with a handicap. Judging by the reports that he got his audience (a claim too embarrassing to make up for no gain), that seemed to work.
That's a big pitfall with analysing Russia: rationalizing stuff happening there to fit a reasonable plan, or at least a coherent overarching narrative, while the plethora of actors constituting Russia couldn't care less about your narrative. They've been improvising with no clear plan for at least a year, on all levels, and it's a miracle we still occasionally see patterns in their collective actions.
... they'd know what exact nasty deeds they're being paid for? How does that help you?
First of all, you need accountable politicians that serve their nation. Age, while it's important, is not of prime importance.