Fred Hechinger was 17 in Eighth Grade when he played the character 'Trevor'.
That was over 6 years ago in 2018.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 24, and has starred in 18 movies in total, 16 of those since Eighth Grade was released.
In Eighth Grade, I think Fred Hechinger looks: