4-7 years seems to be problematic in the sense that the older child just isn't interested in playing with the "baby" - there's no antagonism, it's just that the older child has very different interests.
I can recall myself being 7 years older than my little sister and I almost had no idea who she was until she became an adult. with my brother there was 5 years difference and I just found him annoying for the most part but my sister that is only 14 months younger than myself, we got on great.

Now that we are all adults it's a different story tho, we all get along very well.