[Goose]

If a rule preventing a biological male from competing against a biological female in a certain sport is "arbitrary," then why would not a rule preventing an 18 year old from competing against an 8 year old also be arbitrary?

Yes, of course age cut-offs are arbitrary (if reasonable).  Why does an 8 year-old born on Jan 1, 2013 get to compete in U9, while an 8-year old born on Dec. 31, 2012 have to compete in U10?  It's because you have to set a threshold somewhere and a calendar year was a convenient place to do it.  But it is unquestionably an arbitrary threshold.

BC

Actually BC, my argument would say you don't "nave" to set a threshold if you don't wish to do so. The consequences would be ugly, so undoubtedly a threshold will be set. I don't accept the idea any such thresholds are more "moral" than any other. They are all, in fact, arbitrary.

[Goose]

If a rule preventing a biological male from competing against a biological female in a certain sport is "arbitrary," then why would not a rule preventing an 18 year old from competing against an 8 year old also be arbitrary?

Yes, of course age cut-offs are arbitrary (if reasonable).  Why does an 8 year-old born on Jan 1, 2013 get to compete in U9, while an 8-year old born on Dec. 31, 2012 have to compete in U10?  It's because you have to set a threshold somewhere and a calendar year was a convenient place to do it.  But it is unquestionably an arbitrary threshold.

BC

Actually BC, my argument would say you don't "nave" to set a threshold if you don't wish to do so. The consequences would be ugly, so undoubtedly a threshold will be set. I don't accept the idea any such thresholds are more "moral" than any other. They are all, in fact, arbitrary.