Change color of RadioButtonList based on TextBox value dynamically using JavaScript in ASP.Net

HTML:

<asp:Repeater ID="Repeater1" runat="server">
    <ItemTemplate>
        <div>
            <asp:TextBox ID="txtage" runat="server" onchange="ValidateAge(this);"></asp:TextBox>
            <asp:RadioButtonList ID="IsEligible" runat="server">
                <asp:ListItem Text="Yes" Value="0"></asp:ListItem>
                <asp:ListItem Text="No" Value="1"></asp:ListItem>
            </asp:RadioButtonList>
        </div>
    </ItemTemplate>
</asp:Repeater>

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[1] { new DataColumn("Age", typeof(int)) });
        dt.Rows.Add(18);
        dt.Rows.Add(19);
        dt.Rows.Add(14);
        dt.Rows.Add(20);
        this.Repeater1.DataSource = dt;
        this.Repeater1.DataBind();
    }
}

JavaScript

<script type="text/javascript">
    function ValidateAge(txt) {
        if (parseInt(txt.value) < 18) {
            var tr = txt.parentNode;
            var radiobuttton = tr.getElementsByTagName('input');
            for (var i = 0; i < radiobuttton.length; i++) {
                if (radiobuttton[i].type == "radio") {
                    radiobuttton[i].nextSibling.style.color = "red"
                    radiobuttton[i].disabled = 'disabled';
                }
            }
        }
    }
</script>

Screenshot