My H is two years younger than his older brother, and 11 years older than his younger brother. And H and yBIL have always been close, and still are. My H made an effort to connect with his younger brother, spending time with him on college breaks, always traveling back to his hometown for his younger brother's birthday, no matter what else was going on.
I will agree with PP that for a while my H struggled with some poor choices BIL was making as a young man. H thought that he could share his experiences with BIL so he didn't make the same mistakes. But sometimes people have to go through their own stuff in order to learn...my H realized that and my BIL got himself together and everything is fine now.
Another positive was that as a kid, my H took care of his baby brother...changing diapers, giving bottles, etc. So when we had a baby, my H had more experience doing baby things than I (an only child) did!