In my hospital experiences ...for what reason do you want to do this? You should first consider your own state of health before even to think of this donation! Due to circulatory issues at our age you should seriously reconsider this.It takes us up to two weeks to reconstitute the blood you have donated.With your health not an issue and for the scarcity of blood type you need all that you have.Perhaps.God forbid  ........" YOU"? might need it sooner than you think.May God blaze your path.