It's actually 20 posts and a minimum of 2 weeks membership
Or upgrade your account to platinum
Platinum comes with extra benefits with access to a private area including the platinum classifieds which allow extra non paintball specific trading
Personally I would tend to recommend the use of the two weeks to get a wider overview of what's available, either for new players so that they don't splash out on the first shiney thing
That may or may not apply to you as you are returning, but it's still tempting to buy quickly when you could be getting up to date depending on how long you've been away
Put up some posts around the various areas of the forum letting us know about you, where you played before, what you're into etc and what kind of paintball you fancy getting back into