I don't think there's anything unusual about it, and nothing to be worried about.

I remember I was very interested in comparing myself with other guys. I had an older cousin and we'd go swimming together and I remember being fascinated at how big his dick was compared with mine when we got changed. Later at school it was the same in the showers after football.

Obviously it could be uncomfortable for you, but I don't think you should say anything to him as that will just make him uncomfortable too and might make him think there is something wrong.