I did a search myself and came up with nothing specifically relating to seniors' mental health. Why don't you create a social group on PC, though? You can restrict membership and have your own forum space.

I found two existing social groups:

http://forums.psychcentral.com/group...racefully.html (has a forum)
http://forums.psychcentral.com/groups/over-55-only.html

Not sure if they're what you're looking for.