Student Model

public int StudentId {get; set;}
public string StudentName {get; set;}
public DateTime EnrollDate {get; set;}

List<Student> listOfStudents = new List<Student>();

listOfStudents.Sort((x, y) => DateTime.Compare(y.EnrollDate, x.EnrollDate));

var then = DateTime.Now.AddDays(-7);
var sortedStudents = listOfStudents.Where(s => s.EnrollDate >= then).OrderBy(s => s.EnrollDate);

var today = DateTime.UtcNow;
sevenDaysOldList = listOfStudents.Where(x => (today - x.EnrollDate).TotalDays < 7);

sevenDaysOldList.Sort((x, y) => y.EnrollDate.CompareTo(x.EnrollDate));

sevenDaysOldList.OrderByDescending(x => x.EnrollDate);
// and of course .OrderBy(x => x.EnrollDate) for ascending order

var sevenDaysOldList = listOfStudents.Where(x => (today - x.EnrollDate).TotalDays < 7)
                                     .OrderByDescending(x => x.EnrollDate);