So a new recruit is not allowed to start as a god modder and able to beat a Captain, they will be restrictions for Sword Releases.
For Shinigamis, Shikai can be gained at any rank. Bankai, however, is only avaible to Captains and those Vice Captains approved.(VC won't have mastery over bankai)
For Vizards, Shikai can be gained at any rank as well. Bankai, the user must at least be a Knight.
Finally, for Arrancar, the user must at least be a Privaron to release thier Zanpaktou, though Numeros may still use the Sword while unreleased.