First, you can't get past skill level 225 until your character is level 35. When you qualify, you have to go to Hinterlands and talk to Drakk Stonehand to get Artisan training.
Second, you'll need a fair amount of wildvine to complete the wild leather quests you'll have to complete. Wildvine is a pain to get. It has a poor drop rate and it's expensive on the AH.
Third, you probably won't make much money as a leatherworker, even once you hit the 250 goal. So, if you're trying to power level leatherworking to get-rich-quick, you're probably in for disappointment.
In my experience, the market for most leather goods is really slim. There are a couple nice blues you can make, but it takes a while to farm for mats (or, find/buy the patterns or get the rep up to buy the pattern in the first place). And, once you make those blues, the market is limited (so don't plan on selling a bunch) and people undercut a lot. Another alternative for making money is making armor kits, but these don't require any hard to get mats. So, any leatherworker can make them cheaply, which often results in a saturated market and fickle returns.
Looks like Grollog beat me to it, sorry for repeated info.