I ended up buying the discounted pass last year because my 5 year old turned 6 before the opened. He was not 6 at the time I was trying to register him. When you put in the DOB, it will let you know if it will work or not. I tried and it said he was going to be too old.
This is the fun part. Since he could not get the pre-school pass, I decided to take advantage of the two park fun card for him while it was still discounted. Of course, after I order that, I get a postcard in the mail from BG. It says that since my kid had a preschool pas the year before, he would be eligible for a discounted renewal on the two park fun pass. The discounted renewal was about 20-25 dollars less than the regular discounted price. I contacted customer service and they were able to cancel the original order and refund all of the money except the service charge. I then reordered the pass with the postcard discount.
I added the second paragraph so that people don't make the same mistake I did. If you had a preschool pass last year but don't qualify this year, you may want to wait until the last week before ordering the discounted two park fun pass. You may get a postcard like we did. I think we got the postcard a full month before the other discount was going to expire.
ETA: I just checked my email. The difference was $12. not 20-25.