two questions:

1. What is your standard date display format on your machine? this may affect how that field fills and thus it's capability to react properly.

2. Did you make sure to click the '<>' icon on the top right of the code so as to not copy the code with the line numbers? They can get in the way of things running properly.

EDIT:

Try this as well:

$(function() {
$(document).ready(function(){

// Updated code below
  function updateMinimumEndDate () {
    var minimum = $('.StartDate input').val();
    var minSplit = [];
    minSplit = minimum.split("/");
    var newMin = (minSplit[2]+"-"+minSplit[0]+"-"+minSplit[1]);
    $('.EndDate input').attr('min',newMin);
    alert(newMin);  // Comment this out after you confirm it's showing you the alert, which will indicate this is running properly
  }

  $('.StartDate input').change(updateMinimumEndDate);
});
});

Please clarify, you are saying the date field is displaying in dd-MMM-yy ? If so, then a lot needs to be done to the code:

$(function() {
$(document).ready(function(){

// Updated code below
  function updateMinimumEndDate () {
    var minimum = $('.StartDate input').val();
    var minSplit = [];
    minSplit = minimum.split("-");
    var newYear = ('20'+minSplit[2]);
    if (minSplit[2] > '14')
       newYear = ('19'+minSplit[2]);
    var testMonth = minSplit[1];
    var newMonth = 0;
    switch (testMonth) {
      case 'Dec': newMonth += 1;
      case 'Nov': newMonth += 1;
      case 'Oct': newMonth += 1;
      case 'Sep': newMonth += 1;
      case 'Aug': newMonth += 1;
      case 'Jul': newMonth += 1;
      case 'Jun': newMonth += 1;
      case 'May': newMonth += 1;
      case 'Apr': newMonth += 1;
      case 'Mar': newMonth += 1;
      case 'Feb': newMonth += 1;
      case 'Jan': newMonth += 1;
           break;
    }


    var newMin = (newYear+"-"+newMonth+"-"+minSplit[0]);
    $('.EndDate input').attr('min',newMin);
    alert(newMin);  // Comment this out after you confirm it's showing you the alert, which will indicate this is running properly
  }

  $('.StartDate input').change(updateMinimumEndDate);
});
});

Okay, so the above code will change any year past 2014 to 19_ _ as it needs some way of determining what first two letters to assign to the year field. To change that, change line 10 to reflect the latest possible year it will allow you to set before any number higher will be considered in the 1900's

I cannot even get that to change if i use javascript to change the date format pattern. It simply does not want to work even though I can get the field to look for the pattern you are asking about. It may not be a limitation of Forms but of HTML5