That reason is based on the typical physical differences between the sexes (height, weight, strength, speed, etc).
Many sports are also segmented by age group for the exact same reasons.
The idea behind segmenting across sex and age is to maintain a level of competitive balance and fairness. Yes, there may be some exceptional athletes that show up from time to time. But there won't be a group that is systematically going to have a physical advantage.

I hope we can agree on these points.


I think many male to female trans have distinct physical advantages over their peer cis women that don't come about naturally. Especially if they developed as a male through their teenage years. This gives them a systematic advantage over their peers which is not fair.

For the BYU example, the age group for NCAA is typically like 18-23. Folks in that range are for the most part developed already. So I don't think the 25-26 year old Mormon is going to throw off the competitive balance much here. But if there is evidence of it, I would be willing to swing the other way and say those exemptions should not be granted.