Rhydon doesn't evolve by level. When the Protector is attached to Rhydon, trade it and it will evolve to Rhyperior.
Rhyorn evolves into Rhydon at level 42 which evolves into Rhyperior when traded while holding a protector.
Level 16
On level 20.
level 40
Level 30.
Level 32.
level 26 ^^
Level 16.
At level 59
at level 32
it will evovle at level forty-five
Basically Rhydon doesn't evolve on a certain level. You need to have Rhydon hold a Protector and Trade it, with a another person.