partner-contact/partner_contact_age_range/views/res_partner_view.xml

<?xml version="1.0" encoding="utf-8" ?>
<flectra>
    <record id="view_partner_form" model="ir.ui.view">
        <field name="name">Age Field</field>
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="partner_contact_birthdate.view_partner_form" />
        <field name="arch" type="xml">
            <field name="age" position="after">
                <field
                    name="age_range_id"
                    attrs="{'invisible': [('birthdate_date', '=', False)]}"
                />
            </field>
        </field>
    </record>
</flectra>