public static void Main(string[] args)
{
    var users = new List<User> {
        new User("Ballmer", 60),
        new User("Satya", 49),
        new User("Bill", 60),
    };
    users
        .MaxBy(s => s.Name)
        .Then(s => Console.WriteLine($"Max user = {s}"));
}

public static class LinqExtensions
{
    public static Optional<T> MaxBy<T, R>(this IEnumerable<T> source, Func<T, R> selector) where R : IComparable<R>
    {
        bool isFirst = true;
        T max = default(T);
        foreach (var s in source)
        {
            if (isFirst)
            {
                max = s;
                isFirst = false;
            }
            else if (selector(s).CompareTo(selector(max)) > 0)
            {
                max = s;
            }
        }
        return isFirst ? new Optional<T>() : new Optional<T>(max);
    }
}