My youngest brother is 14 and I am 18 years older than him.
My eldest son is 13, so my brother and my son are more like brothers than Uncle and Nephew... they went through primary school together, and they are now at different high schools... I used to get some strange looks when my son would tell his teacher or friends parents that he and his uncle were punching each other! I would quickly have to explain that his uncle was only 13 months older!!!
I am like a 2nd mother to my brother, but we definitely have a more brother/sister type relationship. I love him to bits and I have never felt as though we haven't bonded like I have with my other brother or sisters... it is actually perhaps a stronger bond because I do look at him as like my son too.