I agree with @happy1 . Wayyyy too early.
Most of the stuff that is in the ACT and SAT is only taught in high school, and most of it is scaffolded on what your kid will learn in middle school.
Seriously, though. Middle school is difficult enough for kids. My kid is amazing and did great on her SATs. I still do not know how we all survived her Middle School years. It’s enough that they go to school, do their homework, and don’t get in to much trouble. Adding “you need to prep for your ACTs which you will take in another six years” is really really not advisable.
That’s exactly what he should be doing
My recommendation is: do not start getting your kid to prepare for the ACTs.
In fact, forget about the ACTs altogether until your kid is in 9th grade. The absolute best prep for SATs and ACTs at this stage is to work hard at his classwork.
Everything that a kid needs to know for the ACTs and SATs is in the school curricula.
Let your kid be a kid. It’s not as though they have a second chance.