No, it is currently not possible to have a level 9 Zekrom, Reshiram, tornadus, ect. unless you hack. They have not given out a legendary pokemon lower than level 20(I think) except for Arceus which was an event for Japan. And looking at the tags, no you can't breed them either.
no it is not unless you have a action replay
You can a level 5 tornadus,thunderus, and landerous, if you Dream radar and cacth them at lvl 5 if you have no bagdes in black/white2 which you can trade to black/white. The only way to trade is to take T-Landerous to Abundent Shrine and you'll get a mirror that changes tornadus,thunderus, and landerous' form.