I too am in this boat and something is amiss. I see that, after posting this, I have posted 2 times. lol, what? I am a lifetime subscriber and a loyal player since beta and have been active in the forums in the past. I can not link my characters nor create forums topics (apparently I am still new according to large bold red lettering at the top informing me:
At this time, you may only post replies to threads that have already been created. After a certain amount of time has passed since your registration date, you will be able to create new threads in forums that allow it.
The Star Trek Online Community Team"
It has been several months since I received a stipend, my tickets are not being answered, emails are auto-reply only so far, and yet if I go to the STO site directly and click on "My Account" I can see my game credentials and play time properly listed, if I click "My Account" from this area I show nothing. Obviously the process of linking my Cryptic account to Perfect World went awry yet I followed the instructions to a letter. Hopefully this is addressed soon as this is just ridiculous.
If you logged into the forums after the changeover some time ago, then it doesn't matter if you've had an account since launch, as far as the forums are concerned you're a new poster and therefore fall under thread creation restrictions.
Once you've met a certain time period after your first login, you should be able to create new threads.
Per this thread that metric is constantly shifting and PWE is not at liberty to disclose the conditions under which that restriction is lifted.
If you feel that you are getting the message in error, please contact support.