odoo-contact-addons/partner_contact_majority/views/res_country_state.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

  <record id="view_country_state_tree_inherit_base" model="ir.ui.view">
    <field name="name">res.country.state.view.tree.inherit</field>
    <field name="model">res.country.state</field>
    <field name="inherit_id" ref="base.view_country_state_tree" />
    <field name="priority">30</field>
    <field name="arch" type="xml">
      <field name="country_id" position="after">
        <field name="majority_age" />
        <field name="same_country_age" invisible="1" />
      </field>
    </field>
  </record>

  <record id="view_country_state_form_inherit_base" model="ir.ui.view">
    <field name="name">res.country.state.view.form.inherit</field>
    <field name="model">res.country.state</field>
    <field name="inherit_id" ref="base.view_country_state_form" />
    <field name="priority">30</field>
    <field name="arch" type="xml">
      <field name="country_id" position="after">
        <field name="majority_age" />
        <field name="same_country_age" invisible="1" />
      </field>
    </field>
  </record>

  <record id="view_country_state_search_inherit_base" model="ir.ui.view">
    <field name="name">res.country.state.view.search.inherit</field>
    <field name="model">res.country.state</field>
    <field name="inherit_id" ref="base.view_country_state_search" />
    <field name="priority">30</field>
    <field name="arch" type="xml">
      <filter name="groupby_country" position="after">
        <filter name="by_major_age" string="Majority age" context="{'group_by': 'majority_age'}" />
      </filter>
    </field>
  </record>

</odoo>