static void Main(string[] args)
{
Customer john = new Customer("John", "Smith", new DateTime(1980, 1, 1), Gender.Male);
Customer David = new Customer("David", "Smith", new DateTime(1974, 1, 1), Gender.Male);
Customer meg = new Customer("Meg", "Brown", new DateTime(1988, 1, 1), Gender.Female);
Customer lucy = new Customer("Lucy", "Johnson", new DateTime(1985, 1, 1), Gender.Female);
var cms = new CMS(new Repository());
cms.AddCustomer(john);
cms.AddCustomer(David);
cms.AddCustomer(meg);
cms.AddCustomer(lucy);
var allAges = cms.GetAverageAge();
var femaleAges = cms.GetAverageAge(x => x.Gender == Gender.Female);
var maleAges = cms.GetAverageAge(x => x.Gender == Gender.Male);
}