从列表中的所有项目中获取特定属性

I have list of Contacts:

我有联系人列表：

public class Contact
{
    private string _firstName;
    private string _lastName;
    private int _age;

    /// <summary>
    /// Constructor
    /// </summary>
    /// <param name="fname">Contact's First Name</param>
    /// <param name="lname">Contact's Last Name</param>
    /// <param name="age">Contact's Age</param>
    public Contact(string fname, string lname, int age)
    {
        _firstName = fname;
        _lastName = lname;
        _age = age;
    }

    /// <summary>
    /// Contact Last Name
    /// </summary>
    public string LastName
    {
        get
        {
            return _lastName;
        }
        set
        {
            _lastName = value;
        }
    }

    /// <summary>
    /// Contact First Name
    /// </summary>
    public string FirstName
    {
        get
        {
           return _firstName;
        }
        set
        {
            _firstName = value;
        }
    }

    /// <summary>
    /// Contact Age
    /// </summary>
    public int Age
    {
        get
        {
            return _age;
        }
        set
        {
            _age = value;
        }
    }
}
public c