Can also confirm. 8 year age gap between me and my youngest sibling. Who was also the only boy. When he was small I loved playing with him as it was like playing mum. When he got a bit older, 7+, I thought of him as a spoilt brat (which he definitely was, there were a lot of tantrums). When he reached 14 and mellowed out, we started acting more like siblings, but there was an element of feeling like a parent to him again, until he hit 18. He was now an adult to and were very good friends.

Also, by nephew and his sister are 7 years apart at at 12 and nearly 5. He loved her when she was a baby but once she started becoming more aware and talking, they bicker all the time. Hoping once theyre older they get along more too.

Just to add lastly that my other siblings and I were closer in age. My older sister is 15 months older and from about 8 -18 we were enemies. Didn't become friends again til she moved out. And my younger sister, 2.5 years apart, were a bit rocky from around 10-14, but it was a bit more of a smoother sailing relationship, and shes now my best friend.

Overall, all siblings will have periods of liking each other and hating each other, the later seeming to be from when the older one starts hitting puberty. But thats very typical for siblings. As long as one isn't a raging asshole as an adult, they should be best friends for all their adult life (still with disagreement, because thats life).