Especially since kids who are working are paying taxes. Not that that should be the singular standard that determines voting rights or anything. But it is common for kids to start working at 16. Sometimes even earlier; I think in my state you can start working as early as 14, even in non-farm jobs, but it's super restricted. So not a lot of employers hire under-16yo.
Like in the other way, we let 18yos vote and we know they're basically still kids. What is it now; our brains our still developing into our mid-20s, possibly even further?
I will say, I don't trust 16yos (or 18yos) with much. But I would feel comfortable with them voting on local and school board issues. Because it directly effects them and they should have a say. We trust them driving independently, for better or worse. We trust them to work, often with money and other goods. Why shouldn't we trust them to vote on these issues?