Gymnastics basic requirements

What level of fitness should one have to be able to start training with fundamental static position like front and back lever?

Are there any requirements? Like being able to do a certain number of pullups and dips...

If you can't do a tuck lever you can try l-sits.

My tip is try to identify what is stoping you from doing the position, and do some specific work then....

Me for example, I was strugling to go from tuck levers to advanced tuck, and as soon as I began working harder on core, (abs, HLL, back arch ups) It came very easly.

Dipping doesn't matter much in either position. It's important to have enough grip strength to hold an inverted position...or you will fall on your head. Many kids and adults who cannot do pullups can still get themselves inverted and hold.

Either FL or BL is more about core/back strength than the ability to do pullups.

If you can't do a hanging bent leg raise, a'body probably wouldn't have much success at either lever. Working skin the cats/360's are important for both movements so you have to be able to do a hanging leg raise.