If you are an oldest sibling, like myself, it is inevitable that eventually your reign of tyranny will become less and less powerful as your younger siblings begin to mature (thus learn to stand up for themselves). However, the simple fact that you are the oldest remains forever. So, while it does eventually stop becoming the only justification for the reason why your younger siblings should bring you water when you are too lazy to do so yourself, or why your younger siblings should be cramped in the middle seat, or why your younger siblings should get the couch in the hotel room while you get to relax in the big bed--it does provide for a unique perspective on your younger siblings that is unlike anything else.
I have two younger siblings, however my brother is only two years younger, and often acts as if he is the older sibling. My sister, on the other hand, is 6 and a 1/2 years younger than me. I still have vivid memories of my 6 year old self jumping for joy when I found out that yes, all my wishing and hoping was worth it, and the new sibling coming in June would be a girl-- a sister-- to my 6 year old self there was nothing better.
The perspective of an older sister is an interesting one, because you get to watch your mini-me grow up in real time. And as they get older you begin to notice things.
You notice that they roll their eyes at your dumb jokes that used to make them laugh. You notice they shut the door when their friends are over when they used to leave it open for you to walk in. You notice they shield their phone from you when you walk behind them when they used to not have a care in the world. You notice they pick out their outfit the night before school when they used to care so little about what they looked like. You notice they put on make up before they go out sometimes, and though they claim it's "just for fun", your heart tugs a little at the thought that they may not think they are as pretty without it. You notice they get wronged by friends--not just in the "she took my crayon" wronged, but truly hurt and have to sit by and watch as they solve their problems by themselves.
But you notice other things too--you notice that they make a joke that leaves you actually laughing, and not in the way that you laugh at a little kid's jokes, but in a way you laugh at a friend's. You notice that they come to you to discuss different things that happen in their friend's lives, and ask for actual advice. You notice that you can FINALLY begin to share clothes with each other, thus each begin raiding the other's closer. You notice that you can both laugh over the fact that neither of you know how to properly put on eyeshadow, so you end up with bright pink eyes. You notice that you can go to them with things that upset you, and they can give you genuine advice. You notice that you don't talk to them how you talk to children anymore, you talk to them like they are grown up. You notice that they are no longer just your baby sister, they are your best friend.
Watching a little sister grow up is one of the most bittersweet things I have yet to experience. You watch her innocence get replaced with knowledge and unscathed heart become a little worse for wear as she maneuvers her way through this rollercoaster called life.
But, there is much more sweet than bitter. You watch her smile and laugh and learn and grow up to become someone you are proud to call your best friend. And you know that no matter what life throws at either of you, you will stand by, support, and love each other forever.