khaale

            List<Person> list = new List<Person>();
            list.Add(new Person() { Age = 20, Name = "Вася" });
            list.Add(new Person() { Age = 21, Name = "Петя" });
            list.Add(new Person() { Age = 23, Name = "Коля" });
            list.Add(new Person() { Age = 18, Name = "Саша" });

            string propertyName = "Age";

            ParameterExpression parameterExpr = 
                Expression.Parameter(typeof(Person), "person");

            Expression<Func<Person, object>> orderByExpr = 
                Expression.Lambda<Func<Person, object>>(
                    Expression.TypeAs(
                        Expression.Property(
                            parameterExpr, propertyName), typeof(object)), parameterExpr);

            Func<Person, object> orderByFunc = orderByExpr.Compile();

            List<Person> sorted = list.OrderByDescending(p => orderByFunc(p)).ToList();

Попробуйте так. По идее должно работать как в L2O, так и в L2S.