Monsters, animal companions, familiars, and character level

[Dustyboy]

Are there equivalents to character level when looking at non-class related creatures?

I have a player asking about his animal companion taking the eldrich heritage fest (elemental)

Its a dangerous precedent though, if so it allows animal ally+boon companion on an animal companion......

If not it makes me wonder about multiple other feats regarding character level and their interactions with certain creatures.

So yeah.....

[Nefreet]

Cohorts are what he'd need. Maybe an awakened animal acquired through Leadership.

Animal Companions, Familiars, Eidolons, and other class-granted critters don't have class levels.

Some creatures in the Bestiaries do, but they're usually called out as such.