My sister is 5 years older than me. That seems like a lot. When I was in kindergarten she was in 5th grade. When I was about to graduate and go off to school she was graduating college and entering the real world. I'm nearing my 21st birthday and thinking about final exams while she is 26 and just bought her first house.
Most siblings that are super close are normally close in age. It's much easier to be close with someone who is in the same life stage as you. When you are going through the same things, it's easier to relate to someone and understand whatever it is that they're feeling.
However, I think that being so far apart in age actually made us closer in the long run. Almost everything that I go through, she's been through it. She can give me advice about how it worked out for her without being involved in a similar situation.
It's much easier to calm you down about finals when they themselves aren't worried about school. Who better to help you deal with mom and dad then someone who already went through all the angsty teen years with them. Getting a job is much easier when they've already had a few and can help you make a resume or help you practice interview questions.
Growing up there are a variety of reasons having a way older sibling is awesome. Once they turn 16, you basically have a built-in free Uber. They can't say no because your parents won't let them. You get to ride around and listen to loud music and look cool in front of all your friends while they're waiting for their mom to pick them up.
Every break-up you ever go through, they know exactly how you feel. They've been dumped. They've done the dumping. They know exactly what you should say. And when your heart gets broken for the first time they already know the cure; ice cream and a movie with your sister.
Every hard thing that you go through, she's probably already been through it. She is living proof that you will survive!
Just because you're in different life stages that doesn't mean that you can't be best friends. It doesn't matter if you're 2 years apart or 5 or even 10+. The age difference doesn't affect how close you and your sibling are. The difference in age gives you two different perspectives on each other's lives. You can help each other more because of your different situations.
I am in college and scared about what happens next, but knowing my sister has done it makes me more comfortable. I love the age difference. My sister is 5 years older than me but has and will always be my best friend.