Вычислить средний возраст по дате, linq

class Department
    {
        public int ID { get; set; }
        public String Name { get; set; }
        public Employee LeaderOfDepartment { get; set; }
        public List<Employee> employees { get; set; } = new List<Employee>();
 
    }
 
  class Employee
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string Position { get; set; }
        public DateTime DOB { get; set; }
        public string Gender { get; set; }
        public double Salary { get; set; }
        public string Department { get; set; }
        public string EmpType { get; set; }
    }
 
        static void Main()
        {
            List<Employee> employees = new List<Employee>()
            {
                new Employee() { ID = 11, Name = "Tom", DOB = new DateTime(1980, 10, 15), Salary =
                15000, Department = "Developers" },
 
                new Employee() { ID = 111, Name = "John", DOB = new DateTime(1985, 10, 15), Salary =
                1100, Department = "Developers" },
 
                new Employee() { ID = 90, Name = "David", DOB = new DateTime(1987, 10, 15), Salary =
                15000, Department = "Designers" },
 
                new Employee() { ID = 49, Name = "Pall", DOB = new DateTime(1989, 10, 15), Salary =
                3000, Department = "Developers" },
 
                new Employee() { ID = 97, Name = "Bill", DOB = new DateTime(1977, 10, 15), Salary =
                9700, Department = "Developers" },
 
                new Employee() { ID = 111, Name = "John", DOB = new DateTime(1977, 10, 15), Salary =
                1100, Department = "Managers" }
            };
 
            List<Department> departments = new List<Department>()
            {
                new Department() { ID = 1, Name="Developers" },
                new Department() { ID = 2, Name ="Designers"},
                new Department() { ID = 3, Name = "Managers"}
            };
 
            //Вычислить средний возраст сотрудников в Департменте Developers
            
 
 
        }

double averageAge = employees.Where(w => w.Department == "Developers").Average(a => (DateTime.Today.Year - a.DOB.Year));

var age = departments
           .Join(employees, a => a.Name, b => b.Department, (a, b) => new
           {
               DOB=b.DOB,
               DepID = a.ID,
               DepName = a.Name,
               EmpName = b.Name
           })
           .Where(w => w.DepName == "Developers").Average(a => DateTime.Today.Year - a.DOB.Year);
 
 
 
            foreach (var n in age)
                Console.WriteLine($" {n.DepName} - {n.EmpName} ");
            Console.WriteLine($"Avg:  ");

            var age = departments
               .Join(employees, a => a.Name, b => b.Department, (a, b) => new
               {
                   DOB = b.DOB,
                   DepID = a.ID,
                   DepName = a.Name,
                   EmpName = b.Name
               })
               .Where(w => w.DepID == 1).Average(a => DateTime.Today.Year - a.DOB.Year);
 
            Console.WriteLine(age);