Exceptional people have a chance of pushing society forward (i.e. creating more resources for the future... exponentially).
(But yeah in general I oppose age-segregated schooling, I think education should have "tracks" (math, physics, sports, music, etc.) and people should attend whatever "level" they're at in each track, in mixed-age groups. And make mostly free (but guided) choices regarding which tracks to put most effort in.)
After all, people with advantages rise to the top, whether that's upbringing, talent, or gene.
But even with the same starting conditions/talent/upbringing/genes, some people will climb further than others. Effort, creativity, etc. We as society should encourage that and reward people who achieve more, for the common benefit of all.
By the way, this is the meritocratic way because we're looking for best people, which includes identifying unrealized talent and then nurturing it.
Instead, the SJW/woke way is "reduce standards until everybody passes", literally https://www.wsj.com/articles/california-leftists-try-to-canc... (a.k.a. everybody equal, everybody stupid akin to Communism's everybody equal, everybody poor)