Not really crazy....are the polish pullets laying yet?
A 'good' cock/erel won't mount a sexually immature(not laying) pullet.
Most young cockerels will try to mount anything they can, including inanimate objects.
Are your older birds submitting to the cockerel?
FYI.....semantics, maybe, but can be important communication terms when discussing chicken behavior.
Female chickens are called pullets until one year of age, then they are called hens.
Male chickens are called cockerels until one year of age, then they are called cocks(or cockbirds or roosters).
Age in weeks or months is always a good thing to note