Beispiel:
string s = "21.02.2005";
Regex reg = new Regex(@"(?<y>d{4})-(?<m>d{1,2})-(?<d>d{1,2})",RegexOptions .Kompiliert);
Match match = reg.Match(s);
int year = int.Parse(match.Groups["y"].Value);
int Monat = int.Parse(match.Groups["m"].Value);
int day = int .Parse(match.Groups["d"].Value);
DateTime time = new DateTime(year,month,day);