To add to what my colleague posted, the average age in our fleet is 31, but perhaps it's easier if I add specific info to our fleet based on the points you summarized.
- Uses Ventrilo (TS is usually meh and sounds terrible)
We use TS3, the quality of our server is good and I've never had any problems with the sound myself, in fact it seems to be more clear then vent. We used to have a vent server but switched to TS3 a few months ago. Perhaps you can judge it for yourself though? I personally preferred vent over TS2, but TS3 seems to work well.
- Fleet is PvE orientated
We have several weekly STF teams running, but we don't focus on just PvE. We also have a big PvP and RP community. Many people in our fleet pretty much do several of those things. Personally I'm not into PvP, but I do like what we get done PvE wise and I set up one of our sub forums dedicated to making groups/ organizing events.
- a fleet that promotes teamwork
Hehe, where would we be without?
- organized leadership
In the 12th we don't believe in the members being there to serve the leadership but that the leadership should function as a management that supports what the members want to do. As such we run an informal command and don't care a lot about fleet ranks.
We are however very organized, our admirals come together on a 2 weekly basis to discuss issues that came up during those 2 weeks and then publish the minutes of those meetings the day after. You can find these back in our magazine too.
- Has a organised fleet website and is the main form of offline communication for its members
www.12th-fleet.com
Our website has over 50k posts and more then 4200 topics, we're VERY active on our website and it's the main thing that ties the entire fleet together.
- A fleet that looks after new players and guides them
One of our sub forums is dedicated to guides/hints/tips/tricks, we also have an academy to help new players out. On TS3 we also have 1 channel dedicated to helping out people and we added a :-) symbol in front of the names of people in random channel that are available to help people out at that moment.
- Accepts people have different ways of doing things and is open to experimentation
Oh boy... Don't get me started on experimentation lol, we're still cleaning up the mess in R&D the last time their admiral had a "brilliant new idea".

I think you'll find yourself quite at home with this point, our forums are constantly developing/ evolving and in just this past week several more sub forums were added to support changes and allow people to do what they like to do.
STO is a living/ evolving game that continues to improve and so is the 12th fleet. If somebody has a good idea it usually gets support quickly and then they put me to work to make it so. :p
For more info please
click here.