I'm trying but I can't come up with a justification for what he said. Maybe SOME kids are interested in sex at 11 or 12....BUT. That is a 4 yr age difference . at 8 that is HALF your lifetime. In child development terms a few years early is an ENORMOUS amount of time.
Also some kids may be interested in sex at that age but I know I wasn't .
I find his need to normalize this stuff disturbing. There is nothing normal about it.