I don't know why they came up with the 34 year old rule myself. I would think they should have some sort of medical test that pronounces you fit or unfit rather than a specific age.

A 25 year old whose been boxing 20 years might have more head injuries than a 35 year old who would like to have their first bout but the 35 year old isn't allowed!

I guess the problem is that catscans are soooo very expensive!