Use the fat kid from Stranger Things and give him the Marvel vitamins lol.It seems like Gunn wants a younger Supes though. but maybe for Batman. I wonder who will play Damian Wayne hey Timothée Chalamet come on down. Granted he's nearly 30 but he still looks like a kid in High School but they might want to go younger but I rather see him as a Teenager/Young Adult.
I really don't know any young actors tbh.
I wouldn't make a good casting director tbh.