In your GetAge method you build the query but forget to run it.
So you should change your code like this:
public string GetAge(string myName)
{
DataClasses1DataContext data = new DataClasses1DataContext();
var myAge = from a in data.Users where a.uName == myName select a;
User user = myAge.FirstOrDefault();
return (user == null ? null : user.uAge.ToString());
}