I just called and FINALLY talked to someone from YES program. Just a recap, I was trying to enroll my 12yo (who will only have been 12 for a couple of months) with my other dd(9) in the Ocean Discoveries class which is for 8-11. We have two little ones who are not old enough to take a class so only one of us can attend with our girls.
The guy I talked to, Dave, said the age cut-offs are FIRM and they enforce them. So, my girls will not be taking the class, I guess

They are so sad.
Many people here in this thread have said that the YES people don't care about the kids being a bit older but apparently they do. I'm so bummed.
Our options are to get a sitter for the little ones but I have never left my babies with a sitter here at home and no way and I doing it at WDW. Or putting them in separate classes at different times but our time is gonna be limited in the park due to having little ones who can't do the parks all day/every day so doing YES on different days isn't gonna work.