Fluter Verifique se a data é maior que outra data

var now = new DateTime.now();
var berlinWallFellDate = new DateTime.utc(1989, 11, 9);
// 0 denotes being equal positive value greater and negative value being less
if(berlinWallFellDate.compareTo(now)>0)
{
  //peform logic here.....
}

Kirk-Patrick Brown