For a mage, 35 is probably the best level to pvp twink. However, I, nor anyone else wouldn't want to give away their whole build, but I'll give you a basic idea.
Stats: full int.
Skills: invest in these skills only depending on how important you think they are. Drain, fire, ice, mana shield, heal, blessing of might, blessing of vitality, lightning. I'll tell you this: max both blessings and fire.
Gear: Voodoo helm, voodoo fire pin, zombies voodoo master robe, brain freeze eye.
Expirement with different combos and find one that suits you and works. Good luck!