How generalizable are training experiences between siblings of a similar age? My brother and I are about 5 years apart, similar morphology, pretty similar run and swim experiences, but a fair difference in bike power, owing to one having more time in the saddle (and racing longer stuff) than the other.

How safe is to Make conclusions like if one type of training “works” for brother #1, it should probably work for brother #2? Or, if another type of training is ineffective for brother 1, it’s probably ineffective for brother 2?