try this
-------------------------------------------------------------
int k = CalculateAge(Convert.ToDateTime("10/25/1982"));
if (k>=18)
{
}
else
{
}
-----------------------------------------------------------------
public static int CalculateAge(DateTime birthdate)
{
int years = DateTime.Now.Year - birthdate.Year;
if (DateTime.Now.Month < birthdate.Month || (DateTime.Now.Month == birthdate.Month && DateTime.Now.Day < birthdate.Day))
years--;
return years;
}
//Via Javascript
<script type="text/javascript">
function age() {
alert("Hii");
var birthDay = document.getElementById("TextBox1");
var now = new Date()
var b_split = birthDay.value.split('/');
if(b_split.length==3){
var birthDate = new Date(b_split[2], b_split[1]*1-1, b_split
[0]);
var years = Math.floor((now.getTime() - birthDate.getTime()) / (365.25 * 24 * 60 * 60 * 1000));
if (years >= 18) {
}
else {
}
}
}
</script>
<asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="javascript:return age();" />