Hi from the dad of an ROTC participant who is also a commercial pilot. Your question has a couple of layers to it- are you already in a unit or just learning about the AF while in HS?
Regardless, I'll try to provide some details you may find helpful.
1. You can participate in AFROTC (or any ROTC) and major in Aeronautical Science with Flight in college (or like flight degree program) at Purdue or others and complete your flight training for a private, instrument, commercial, CFI/ CFII/ CFMEI/ Multi-engine and foundations toward your ATP licenses while in ROTC. But AFROTC even for those on any of their TYPE scholarships as a standard does not pay for those flight costs - it will be in your own dime. And it isn't cheap. Some argue why not just wait and have the Air force / Navy/ Army to train you to fly for free after graduation? You can, but * and this is key, *not everyone who wants to fly ends up as a pilot - most AF officers are NOT pilots fyi.
2. Ask your unit if they have funds or a program for you to pursue your private license (PPL) or flight hours. Ask your HS and or college the same thing. or get a job and start saving and pay for it yourself like my DS did.
3. In HS, college on your own time you can pursue your licenses at a local airport and gain hours of flight experience. Some scholarships available- you can find them/ pursue them. Just be aware these paths can take more flight hours - a lot more time to complete.
4. High schoolers can also pursue hours toward a private more affordably through programs like Civil Air Patrol "Wings" or power fight academies.
5. Recommend getting an advanced flight physical by someone qualified to give one early so you can rule out any problems that might negate you being able to be a military or commercial pilot. Better to know sooner than later.
In year's past there was a measurable/ specific/ noted advantage of flight hours for flight slots when commissioning in the AF- please confirm if that is still the case. There was some buzz last year that it offered an unfair advantage to the privileged so there was talk of negating that advantage and no longer counting hours for or against... I don't know the latest position on this but I'm irrelevant in a sense on this - but you should confirm. Just be aware of what those hours will, and will not get you so you know.
I think other than an introductory flight all hours should be in a program structured to get you a license. FYI even AF Academy cadets do not get much more than a private license in their 4 years. Shocked me to learn that.
Good luck in your pursuit to become an AF pilot and thanks for your willingness and passion to serve.