Gotta agree with PP - not wanting to spend time with younger sibs would probably turn my decision into a definite "you're going"...my oldest gets annoyed by her youngers sibs every now and then now, and we are always reminding her that she was just as annoying at their age and mom and dad dealt with her...and her younger sibs go along to make things possible for her now (like sitting and waiting for her 2 hour class to finish once a week), so she can do the same for them...the sibling relationship is such a key one for life and realizing that it's not "all about you" as a teen, but you now have some "adult" responsibilities and not just "adult" privileges, is such an important thing for teens to learn and internalize...and some of those responsibilities might not have any immediate payoff for you right now or even any payoff later...some things you do b/c they are right and occasionally entertaining one's younger sibs to help out mom and dad is one of them...as a bonus, years from now, those sibs will probably grow up to idolize you if you put in the effort now...and they may be the ones who have to look after you when you're old and grey...
Now, that's not to say the oldest always gets stuck playing the martyr 24-7...that's where mom and dad step in. With the ages of your younger kids, you know when they've already had time with their older sibling and when it's time for you to step in to entertain them and/or for you to step in and tell the younger that he/she can entertain themselves. Family balances the needs and wants of family.