This is only in reference to MHA characters that Yagami Yato made audios for. The main characters we see are adults recounting the past. We see them as teenagers because it's a flashback. She makes audios about their canon adult versions we haven't seen yet.
The very first episode involves Deku saying, "This is the story of how I've became the world's greatest hero."
Being a hero is a job occupation in this world so not only did he graduate high school but fully mastered his quirk at this point. And raised up the hero ranks due to hard work and popularity so this probably took a few years making him an adult at this time.
If you dislike Yagami's content that's fine. Unfortunately, there is a lot of disinformation about her and if the person who accused her of grooming them is genuine then I fully encourage them to contact authorities. Point blank. End of story.
A twitter user who claimed Yagami Yato was a groomer blocked me after I disagreed and offered a resource titled "Everything You Need to Know About Online Grooming" by the Innocent Lives Foundation.
This is an organization dedicated to capturing online predators and I was blocked for sharing it.
I'm a mandated child abuse reporter in the state of PA and I'm telling you Anti-YY's are fucking disgusting -- one of them on twitter said she dreamed of brutalizing her. If someone tells you they don't like yy for an easily disproven reason, run.
On twitter, I see people spreading rumors and this shit is going to discourage any actual victims of grooming because kids are trying to cancel Yagami Yato. This is a game to them.