No you need the national dex.
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Provided you have the national Pokedex. Yes.
It won't evolve because you don't have the National Pokedex. Once you have the National Pokedex, which you get after beating the Elite 4, catching 60 different species of Pokemon, and completing the Sevii Islands sidequest, you'll be able to evolve your Golbat.
It depends on the Pokemon you're trying to evolve. While some Pokemon can evolve without any problems due to being in the regional Pokedex, other Pokemon (Golbat, for instance) won't evolve without the National Pokedex. Note that this is only the case in FireRed and LeafGreen - in later games, Pokemon not in the regional Pokedex will evolve, but won't be recorded until you get the National Pokedex.
Golbat does not evolve at any specific level. You need to get the Golbat to like you a lot and then when it levels up it should evolve into Crobat.
Golbat doesnt evolve by level, you have to trade it for it to turn into Crobat.