Considering the developments of season 5, I am thinking that Red John is either:

1) Ray Haffner (his connection to visualize) 
2) Robert Kirkland (his conversation with Jason Lennon before killing him, conversation in the limo when Jame got hired by CBI)

Both of them fit the criteria:

1) Shook hands with Patrick Jane
2) Have easy access to people of influence 
3) Approximate age

Looking forward to seeing how this develops.