Why are some powers restricted and others can be had at any time? New members are often disappointed to see a favorite power from the series falls into this category- and it's easy to see why. There are some excellent powers here, no doubt about it. But as a famous superhero once said, with great power... comes great responsibility.
What does that mean? It means that the powers listed here, while limitable (see What makes a banned power? for a discussion of limitability in powers) are nonetheless extremely strong in their own right. Many times they are so-called "umbrella" or "cluster" powers that give the user many, many options in the RP. It can be very cool. But in the wrong hands, it can suck the fun out of the RP for an unlucky person- and we want to avoid that at all cost.
Powers, however, do not abuse themselves. They are abused by players. This in mind, restricted powers are permitted on the condition that we get to know you first. If you have an investment in the site, if you've spent time plotting and talking in cbox with everyone, we can know with much more certainty that you're not a spammer out for quick lulz with a power. RPing is, ideally, never about the powers and always about the characters. Sometimes people come to the site with that the wrong way around. That's OK. 250 posts is plenty of time to learn. That's part of the idea too- accidents happen, rules are broken and feelings are hurt without any intention to do harm. 250 posts is training, a way to integrate yourself into the grand scheme of things so that when the time comes, you can play on the higher levels in a way that will be fun for everyone involved.
So if you have less than 250 posts, don't despair. You'll get there. I'm not saying you should spam posts just to get there quickly- that would destroy the point I gave above. Take your time. Bask, talk, and learn, and eventually you'll get your chance. Anyone can make a great a character. Give us your best, and we'll give you ours. That's a promise.