date_issue.rb

          <div class="form-group">
               <%= f.label :from_date, "From Date", :class => 'control-label col-md-2' %>
                 <div class="col-md-10">
              <%= f.text_field :from_date, :class => 'form-control date', :placeholder => "Start Date", :value => "#{ f.object.from_date.nil? ? " " : f.object.from_date.now.strftime("%m/%d/%Y")}" %>
        </div>

      def expiration_date_cannot_be_in_the_past
        if expiration_date.present? && expiration_date < Date.today
          errors.add(:expiration_date, "can't be in the past")
        end
      end  

Here expiration_date is the date field , so check with debugger weather you are getting date on it or not if you are getting that then check this condition, it should work but how you have implemented it is looking like you are checking wrong attribute. As I can see you don't have date field with the name of expiration_date.