To get the total seconds. Try the following.
var testString = "2Y 4M 3D";
var splitString = testString.Split(' ');
var year = int.Parse(splitString[0][0].ToString(CultureInfo.InvariantCulture));
var month = int.Parse(splitString[1][0].ToString(CultureInfo.InvariantCulture));
var day = int.Parse(splitString[2][0].ToString(CultureInfo.InvariantCulture));
var totalSeconds = (DateTime.Now.AddYears(year).AddMonths(month).AddDays(day) - DateTime.Now).TotalSeconds;
solved DateTime Format user entries