Trans Olympic athletes: Imagine if Jenner was 40 years younger

Since watching the 2016 Summer Olympics, and especially the commercial with the trans male athlete, it made me ponder on Jenner and his/her history with the Olympics. Now in the commercial I saw, supposedly one of the athletes (possibly cyclist?) for Team USA is a trans male, which is a woman transitioned into a man, so to be able to compete on the same level as other cis men, I'd say good for him.

To get back to Jenner though, it just made me ponder, imagine if Bruce Jenner had been 40 years younger when he had decided to begin his transition into Caitlyn Jenner (at least to the point s/he's gotten so far), or 25 rather than 65, and THEN decided to compete in the Summer Olympics in the Women's Hepthalon or whatever...Would that have been fair? And/or would it have even been legal? Especially considering he'd waited until after male puberty to be even begin the transition, thus acquiring male hormones & musclecture that the cis female competitors wouldn't naturally possess without illegal steroids, hormone therapies etc.