I have no idea to do that. Did you try this?
<%= simple_form_for @user do |f| %> <%= f.association :ages, :as =>
:check_boxes, :required => true %> <%= f.input :other, :as =>
:check_boxes %><%= f.input :other, :label => false %>
<%= f.button :submit %><% end %>
I don't know other way to build something as you want. Just try and tell us
how can you solved this.