Open locale-enUS.mpq and extract Constants.lua from there.
You will find these from there:
--
-- Talent
--
SHOW_TALENT_LEVEL = 10; <-- edit this to the level that you want the talent window to be available
SHOW_PVP_LEVEL = 10;
SHOW_LFD_LEVEL = 15;
Then you save it and patch it. In addition you must do what Tommy said in the core, else you won't get points even if you have the window available at 1 (also they won't save up even if you add them manually, the core removes them at every logout if you are under 10)