=f.label :date_of_birth
=f.date_field  = :date_of_birth

=f.select(:month, [ 'January', 'February', 'March', 'April','May', 'June', 'July','August','September','October', 'November', 'December' ], :prompt => "Select Month")
  =f.select(:year, [ '1988', '1989', '1990', '1991', '1992' ], :prompt => "Select Year")
  -:date_of_birth = :month + :year