Question: what level should i evolve eevee into leafeon?
Answer: Well, it depends on what moves you want for your Leafeon; if you wanted a Baton Pass Eevee team then you need your Eevee to learn Baton Pass at Level 33 (36 in BW). Otherwise, you can evolve your Eevee as soon as you want if you won't use any of Eevee's level up moves.