Each species would have evolved its own characteristics regarding this. I wouldn't say this (what you have suggested) is NOT true for all species. It is certainly describes the cat family where the dominant males will kill off defenseless male kittens. (You can see it is easier to remove competition at this age rather than after they have grown up.)
With humans who descended from Ape like ancestors, do apes behave like this? Don't they have a more inclusive society keeping the younger males there in the group in case of "war" with rival clans.
It would depend on the needs of the species and what produces the best survival value.
how true
however
let us examine the practices of the forest people(pigmys) of central africa.
at puberty, the young males are forced out of the tribe to a "young men's tribe" where they live away from parents and relatives until
they are invited to become adults, and go through some rather painful rituals. Once done, they are invited to rejoin the tribe, find a mate, and live as a member of the tribe. (some do the ritual thing first, then the young men's tribe) The young women do not leave their families until wed.
This has the advantage of creating a very stable society. When young men have reached the age wherein they need to rebel, they do not rebel against society, they rebel back into society.
Lion males do not kill their own offspring. But it is common for them to kill the cubs of the previous male head of the pride.
Still, as the young males grow, they are encouraged to leave the pride, and roam alone or in the company of another young male until they can join a different pride. Females ain't treated this way.
While this behaviour does not hold true for all species, nor for all the time, it is well rooted in certain societal behaviours for our species as well as for others.
Knowing that there is a tendency toward sexism, however does not mean that we, as humans, can do no different.
(anecdote)
When I was in grade school, I was terrible at ball sports. There was a girl(Terri) in my class who was far and away superior to me and most of the guys when playing baseball. We had a system wherein the "team captains" had to chose teem mates in rotation. Some of the guys were already sexist, and when I had to choose opposed to one of them, I would have the freedom to choose the better guys first,(knowing that he would not chose terri till all the guys were chosen) then when we were down to one guy left, I'd chose Terri.
Whenever anyone choses team mates, collegues, or employees based on sex, they have earned the right to lose.