ASP.NET

public partial class Default1 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        List<Person> people = new List<Person>();

        people.Add(new Person() { FirstName = "Gill", LastName = "Julian", Age = 20 });
        people.Add(new Person() { FirstName = "Hill", LastName = "Andrew", Age = 19 });
        people.Add(new Person() { FirstName = "Hart", LastName = "Brett", Age = 24 });
        people.Add(new Person() { FirstName = "Dwight", LastName = "Jane", Age = 20 });
        people.Add(new Person() { FirstName = "Gary", LastName = "Gray", Age = 18 });
        people.Add(new Person() { FirstName = "Prim", LastName = "Anne", Age = 19 });

        List<int> distinctAges = new List<int>();

        //get a list of distinct ages from 'people' list
        foreach(Person person in people)
            if(!distinctAges.Contains(person.Age))
                distinctAges.Add(person.Age);

        //wonder whether there is a delegate I can use to do the above
        //Like: distinctAges = people.FindAll( delegate ...
    }

    public class Person
    {
        public string FirstName;
        public string LastName;
        public int Age;
    }
}