Adding nested attributes to Devise "Edit profile" view

edit.html.erb

<h2>Login Details</h2>

<%= form_for(resource, as: resource_name, url: registration_path(resource_name), html: { method: :put }) do |f| %>
  <%= devise_error_messages! %>

  <div class="field">
    <%= f.label :email %><br />
    <%= f.email_field :email, autofocus: true %>
  </div>

  <% if devise_mapping.confirmable? && resource.pending_reconfirmation? %>
    <div>Currently waiting confirmation for: <%= resource.unconfirmed_email %></div>
  <% end %>

  <div class="field">
    <%= f.label :password, "New password" %><br />
    <%= f.password_field :password, autocomplete: "off" %>
  </div>

  <div class="field">
    <%= f.label :password_confirmation, "New password confirmation"  %><br />
    <%= f.password_field :password_confirmation, autocomplete: "off" %>
  </div>

  <div class="field">
    <%= f.label :current_password %> <i>(to confirm changes)</i><br />
    <%= f.password_field :current_password, autocomplete: "off" %>
  </div>

  <%= f.fields_for :profile do |builder| %>
    <hr />

    <h2>Profile Details</h2>

    <div class="field">
      <%= builder.label :name %><br />
      <%= builder.text_field :name %>
    </div>
    <div class="field">
      <%= builder.label :age %><br />
      <%= builder.text_field :age %>
    </div>
    <div class="field">
      <%= builder.label :hobbies %><br />
      <%= builder.text_area :hobbies, :rows => 5  %><br />
    </div>
  <% end %>

  <div class="actions">
    <%= f.submit "Update" %>
  </div>

<% end %>

<%= link_to "Back", :back %>