Honestly one of my favorite parts in Vigilantes is how AFO was trying to discover any secrets behind Koichis strength and couldn't find anything. Hes was just so confused as to how normal Koichi is that he honestly couldn't wrap his head around it.
That was funny when you stop to think about it, but gonna be honest, Koichi is not what I'd call normal. Far from it in fact, and that was talked about in Chapter 18 completely offhandedly
Koichi started using his quirk when he was still a little baby, he barely had hair, he couldn't even walk, just crawl by the looks of it.
The main story did say that non-heteromorphic powers start to manifest around the 4-years mark. Sure, they can show up before, but that's extremely rare, the only person I can think that might fit that criteria is Eri, as revealed in chapter 156 of the main series
And even so, it could be she's around 4 there, it's just her quirk is incredibly powerful because she's past the singularity point
So, Koichi is definitely not normal, at least when it comes to quirks. He's an extreme prodigy.
There is also this guy











