Hmm, 25 is a little low for most of the places where I like to find it...
The best bet would probably be to type iron deposit in the search box to the left, look at the list of places where it can be found, and pick a zone that you are comfortable moving around in. Then check the map for the node locations and take off. There are some spawns in the Wetlands that you might be able to get to if you're careful (a cave in the North full of dinosaurs has a few, and there are some around the edges of the orc valley, but my guess is you're going to have to level up some before you can mine much iron.
Iron can be found fairly regularly in parts of Darkshire, which should be easy enough for you to get around in. It can also be found, albeit somewhat more rarely, in Redridge.
I was wondering, where is the best place for a lvl 25 dwarf to mine iron?
As has been stated in MANY, MANY other posts, you should learn to use the search feature here on Alla. See the white box in the menu to the left? Type "Iron Deposit" there, and press enter.
Unlike the Search option,my ideas of finding things are specific,yes,lv 25 is too low for iron,try hitting the 30's . The BEST place for iron is uldaman,you'll have frequent spawns,not to mention few extra other ore's,and the occasional truesilver,i suggest grouping through it at the proper lv to get decent iron.
There is a lot Iron in Duskwood and The Wetlands, but they are guarded by Level 27+ mobs. In these areas its always guarded by or close enought to aggro the main camp.
In Duskwood theres a vein right behind the Dark Runner Worgen camp. You will pull at least two at a time to clear the camp so bring a friend. The cool thing is that the worgen give up medium to heavy leather for skinners and have decent drops as well as getting the XP for killing them.
In The Wetlands there's one in the Dragonmaw Camp but this one you can get to without aggroing the main camp.
There's more than these of course but these two are consistant and respawn often.