//11

List<DateTime> Dates = new List<DateTime>
{
    new DateTime(2011, 09,07),
    new DateTime(2018,03,15),
    new DateTime(2015,05,19),
    new DateTime(2022,07,15),
    new DateTime(2009,02,25),
    new DateTime(2021,09,16),
    new DateTime(2001,06,29),
    new DateTime(2024,03,04)
};

DateTime today = DateTime.Today;
DateTime date1 = Dates[0];
TimeSpan date2 = today - date1;

foreach (DateTime date in Dates)
{
    TimeSpan difference = today - date;
    if (Math.Abs(difference.Days) < Math.Abs(date2.Days))
    {
        date2 = difference;
        date1 = date;
    }
}

Console.WriteLine("Ближайшая дата: " + date1.ToShortDateString());