Because graduation is ALWAYS before July of each year; just realize that you CAN'T be 27 years old when you GRADUATE. (Except for rare circumstances)
Look at it like the store that shows that the sign "YOU CAN BUY CIGARETTES IF YOU WERE BORN BEFORE THIS DATE". In this case it's the opposite.
"YOU CAN GO TO THE MILITARY ACADEMIES IN 2008 IF BORN AFTER:"
JULY 1st 1985
"YOU CAN GO TO THE MILITARY ACADEMIES IN 2009 IF BORN AFTER:"
JULY 1st 1986
Basically, if your birthday is June 30th 1985 or earlier, you CAN'T go to the academy.
P.S. It doesn't need to mention the max age at graduation, because unlike a traditional school you HAVE to graduate in 4 years. There are exceptions for 4 consecutive years due to injury, health, academic waiver, etc... but you only get 4 years to get your degree. It is possible to be 27 years old at graduation.