using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var people = new[]

        {

            new Person("Johan", 37),

            new Person("rightfold", 12)

        };

        var averageAge = people.Average(x => x.Age);

        Console.WriteLine($"{string.Join(",", people.Select(x => x.Name))} have average age: {averageAge}");

​

    }

}

​

public class Person

{

    public Person(string name, int age)

    {

        Name = name;

        Age = age;

    }

    public string Name { get; }

    public int Age { get; }

}