Section 2851. Age not to be bar to employment by public authorities

No
  public  authority  shall  hereafter  prohibit,  prevent,  disqualify  or
  discriminate  against  any  person  applying  for  employment  by,  such
  authority, who is physically and mentally qualified, or from  competing,
  participating  or registering for a position, or be penalized in a final
  rating for any position, by reason of his or her age. Any existing rule,
  regulation, penalty or requirement resolution preventing the  hiring  of
  persons  because  of  age  shall  be  void,  except  that nothing herein
  contained, shall prevent any public authority from  adopting  reasonable
  minimum  or  maximum  age  requirements for positions such as policeman,
  fireman, guard or other positions which require  extraordinary  physical
  effort except where age limits for such positions are already prescribed
  by law.
    Notwithstanding  any  provisions  to  the  contrary,  no person who is
  physically or mentally qualified may be  disqualified  from,  competing,
  participating  or  registering  for  a  promotional  examination  or  be
  penalized in a final rating or barred from promotion after having passed
  such promotion examination by reason of his or her age,  by  any  public
  authority.