I used to be a part of the Smash community and the issue is admittedly a very convoluted and complex one.
The community is extremely grassroots. Nintendo doesn’t really run the community in any major way and has often found itself at odds with the community, trying to cancel major tournaments of theirs on a whim, and as such it’s somewhat self-contained. The community runs the community, sets its guidelines, determines what is and isn’t allowed, etc. And for the most part, the vast majority of the competitive Smash playerbase started competing when they were extremely young themselves, even as far back as the early 2000s when Melee started picking up steam.
A lot of the best Smash players in the world - be they Melee or Brawl/4/Ultimate players - began competing when they were very young, competing against people who were slightly less-young. Much of the Brawl community that played when they were teenagers, or Smash 4 players who picked up the game in their early or late teens, are now adults while younger players are picking up Ultimate all the same; the guys who competed in Brawl, unless they got banned or retired, are still competing in Ultimate today. Hell, we’re about to reach the point where there are top-level Ultimate players who weren’t even born when Brawl comes out.
But, of course, the community being so grassroots means it’s also quite unregulated compared to Street Fighter (the definitive Fighting Game franchise, which Capcom has a lot of influence over) or League of Legends (which Riot pours massive amounts of money into), and even those communities have their fair share of questionable or even illegal stuff going on. 99% of the time there aren’t any pedo problems in the Smash community and young and old players alike compete on equal footing, but that 1% of the time where questionable and illegal stuff does happen becomes a massive problem.
And the problem is, you can’t realistically “segregate,” for lack of a better word, the playerbase retroactively. That never happened back in the early 2000s, and it can’t happen in 2022. Good players only get good by playing against other good players; imagine a world where a 15-year-old MKLeo (now the undisputed best Ultimate player and a top 5 Smash 4 player by the time he could travel) couldn’t compete with half of the Mexican Smash scene or go toe to toe with top-level players like the now-disgraced ZeRo back in Smash 4. ZeRo himself, as a minor, learned under Smash veteran Mew2king back in the Brawl days and even got very good at Melee before becoming the most dominant player not just in Smash history but also in esports history back in Smash 4. Imagine if top Smash 4/Ultimate player Tweek couldn’t compete with many top players? Imagine if sparg0 now couldn’t compete with MKLeo and Tweek because he’s only 16? That opens up a HUGE can of worms because now you’re punishing players for their age when they can and occasionally do compete with older players; hell, there are even players in their late 20s and early 30s still playing.
So what’s a grassroots community to do? Well, there isn’t a definitive answer.