My sister and I have a pretty tiny age gap. We are solid two years and four months apart in age, and that meant we spent a lot of time playing together as kids. Often, her friends were my friends, and my friends were her friends, too. We had neighbor kid friends who were also sisters; one was a year older than her, and the other was a year older than me, and we were literally the perfect friend group.
While we had fun together, there were many times when we needed a break from one another. As the older sister, it's no fun to be trying to hang out with your friends when your younger sibling can't get the hint that they're not wanted. That's annoying when they're two years younger, but it would be so much worse if they were eight years younger, which is precisely what is happening to the niece of this Redditor.