hmm... i graduated highschool in '02 so forgive me if i get some of the details muddled up, but just apply as applicable to your situation.
let's start with the college search first. from my high school, i think most students begin during junior year if not the second half of their sophomore year. so here is a list straight from Apple's website
http://www.apple.com/jobs/us/students.html that details which universities and colleges they recruit from. cross check this with that US News report which ranks colleges. obviously the higher rank, the more likely you will stand out in the applicant pool... however this also depends on your current GPA range
apologies if i was not clear earlier on the jobs availability. i was looking from the perspective of once you get into university / college, you can study other majors and still get internships with Apple. so as a 16 year old, no... there will not be any of these positions open but once you are a sophomore you should explore these possibilities
what do i recommend? my recommendation is the same as
@ncstatered21 focus on getting into a good school (preferably something on the Apple list) and rock your first year GPA where classes are the easiest.
where my thoughts deviate from the many on this forum is that i do not recommend pursuing Apple retail. i do not know your financial situation so do take what i say and think if it makes sense for you.
working retail* in general is a waste of time during college. you are spending at least 20 hours a week (assuming part-time hours) putting your efforts into a profession that will maybe give you two bullet points worth writing about on your resume. your dream is to work in Apple corporate right? maybe manage a product line, maybe analyze their supply chain capabilities, maybe code the next iOS etc.
your time is better spent joining the right clubs and groups in uni / college. a lot of these schools bring in alumni from different companies to come speak to students... this is essentially unofficial recruiting. you should maximize face time with these people and start networking. they may also do company campus visits, volunteer programs etc. to me, this is where i think your effort will produce the most results.
retail makes sense on first blush because a lot of people think that having worked at "Apple" surely means you are ahead of the game right? well keep in mind that you are likely competing with student from Berkley / UIUC/ CalPoly who has done a campus visit, did an alumni meet and greet, competed in a Microsoft sponsored case competition with their club... i will tell you that those type of experiences catches the eye of recruiters more so than any other retail job
one last thing. retail, or sales in general, is one of those jobs that has a tendency to pigeon hole you early on in your career... that is because you do not gain any particular hard skill set (e.g. coding, financial analysis etc). now if retail is your thing, then ignore everything i said above. if your finances dictate that you must hold a part-time job during college, ignore what i said
i meant "quant" as "quantitative" meaning needs a lot of math. Apple and many other tech companies focus a lot on quantitative skills during interview because it is a very easy and fast way to weed out resumes and candidates. just something to think about when you applying for jobs with tech firms
as for the Apple retail in during college question, i refer back to what i wrote above. long story short, i think you can use your time more efficiently on other activities that can put you in a better position to get in Apple. don't worry about the undergrad or masters comment... in retrospect, it is not applicable to your situation for quite awhile
*note: be wary of other jobs that target college kids, waitering, bank teller, that sort of thing