i'm the youngest in my family. my brother is 14 years older than me, and my sister is 10 years older. it's not weird at all, they've always been awesome to me. they would take me places like shopping and to friends places, hang out with me, teach me things.
so, it's not weird. my oldest brother, who i've never really met, he's 36 now and i'm 18. you're never too old to be an older sister.
obviously, i can't really tell you what itll be like from your position as the oldest, but as the youngest with siblings much older than me, it's actually a really cool experience.