I met a cadet at Norwich University who enlisted in the Army Reserve his junior year of high school and did BCT during the summer. This is something I would might want to do but I don't turn 17 until August 9th. Would this be too late and deem me ineligible for this option?
You could not enlist the day you turn 17. There is lots of paperwork and processing that needs to be done prior to that which you cannot begin until you turn 17. Either way, you will not turn 17 until after your penultimate summer, so you'll be ineligible for split op as it pertains to high school. You'll attend BCT and AIT after you graduate.