Controlling Bot Access & Indexing of Pages

Hi,
I have a private forum, or I thought so, I didn't realise that the Google Bots Index and Cache my pages. I'm working on removing Cached pages, but I'd like to know if there is the function in my forum to make it completely private. I don't see anything in Security or Configuration that can be changed.

It's just a small communication group and is used purely for personal use. I do not need to direct traffic to my site, or need for anyone to know it exists, permissions are set up so that only approved members are able to see my threads and posts.

Can anyone help me, I'm worried about my private discussions being made freely available
Thank you!

Note that my forum was set up around 2010, maybe there is a more recent version I should have that will help with settings?

Sorry for double posting. Thank you for the instructions