Calculate Relative Time: Time Ago in words in ASP.Net

Here I have created sample that accepts from date and to date and on submit shows the message like "a minute ago", "an hour ago", "Three weeks ago", etc...

HTML

<cc1:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</cc1:ToolkitScriptManager>
<div>
    Enter From Date : &nbsp;&nbsp;
    <asp:TextBox ID="txtFromDate" runat="server" />
    <cc1:CalendarExtender runat="server" TargetControlID="txtFromDate" PopupPosition="Right">
    </cc1:CalendarExtender>
</div>
<br />
<div>
    Enter To Date : &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <asp:TextBox ID="txtToDate" runat="server" />
    <cc1:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="txtToDate"
        PopupPosition="Right">
    </cc1:CalendarExtender>
</div>
<br />
<div>
    <asp:Button ID="btnGetAccurateDifference" Text="Get Accurate Difference" runat="server"
        OnClick="btnGetAccurateDifference_Click" />
    <br />
    <br />
    &nbsp;&nbsp;<asp:Label ID="lblMessage" runat="server" />
</div>

C#

protected void btnGetAccurateDifference_Click(object sender, EventArgs e)
{
    this.lblMessage.Text = this.GetAccurateTimeDiff(Convert.ToDateTime(this.txtFromDate.Text.Trim()), Convert.ToDateTime(this.txtToDate.Text.Trim()));
}

private string GetAccurateTimeDiff(DateTime startDate, DateTime endDate)
{
    TimeSpan timeSpan = endDate - startDate;
    int years = endDate.Year - startDate.Year;
    int months = 12 - startDate.Month + (years - 1) * 12 + endDate.Month;
    if (startDate.AddYears(years) > endDate)
        years--;
    startDate = startDate.AddYears(years);

    if (startDate.Year == endDate.Year)
        months = endDate.Month - startDate.Month;
    else months = 12 - startDate.Month + endDate.Month;
    if (startDate.AddMonths(months) > endDate)
        months--;
    string message = string.Empty;
    int weeks = timeSpan.Days / 7;
    int extraDay = timeSpan.Days % 7;
    startDate = startDate.AddDays(weeks * 7 + extraDay);

    timeSpan = endDate.Subtract(startDate);
    int days = timeSpan.Days;
    int hours = timeSpan.Hours;
    int minutes = timeSpan.Minutes;
    int seconds = timeSpan.Seconds;

    if (years > 0 && months > 0 && days > 0)
    {
        message = years + " years " + months + " months " + days + " days ago";
    }
    else if (years > 0 && months > 0)
    {
        message = years + " years " + months + " months ago";
    }
    else if (months > 0 && days > 0)
    {
        message = months + " months " + days + " days ago";
    }
    else if (months > 0)
    {
        message = months + " months ago";
    }
    else if (weeks > 0)
    {

        message = weeks + " weeks ago";
    }
    else if (days > 0)
    {
        message = days + " days ago";
    }
    else if (hours > 0 && minutes > 0 && seconds > 0)
    {
        message = hours + " hours " + minutes + " minutes " + seconds + " seconds ago";
    }
    else if (hours > 0 && minutes > 0)
    {
        message = minutes + " minutes " + seconds + " seconds ago";
    }
    else if (minutes > 0 && seconds > 0)
    {
        message = minutes + " minutes " + seconds + " seconds ago";
    }
    else if (minutes > 0)
    {
        message = minutes + " minutes ago";
    }
    else
    {
        message = seconds + " seconds ago";
    }
    return message;
}

Screenshot