I played as a Ret all the way up to 61, and had no real problems at all. I was going to STAY Ret for the most part, buy my guild has a few other Paladins that are just a few levels behind me that want to stay Ret, so I respecced to Prot about half way through 61, and have been tanking Ramps and BF since then for practice. At first I did this with "guild only" groups with at least one person that knew the dungeons well and could mark pulls for me. Then I started doing some PUGs and marking targets for myself. I have gotten good reviews from the PUGs I have done so far... so now it is time to do some research and get some guild help and start on Underbog!
Tankadins seem to be in REALLY high demand lately, but even if that is the way you want to go, being Ret until you hit outlands won't hurt you a bit. If you do go Prot after that, there are numerous places to study up on the dungeons (and later the raids), and being in a good guild with some people that have already "been there and done that" (and are willing to teach you) helps tons too.
Until you hit outlands, just put on the best gear you can for your level without breaking the bank. Once you hit outlands, start keeping the quest rewards and drops that give you the best stats for your chosen tree.