Teach him up to the level you’re comfortable with! Japanese 101-level stuff is super easy to teach, even for a non-native Japanese speaker. Just teach a few words and phrases, Jikoshoukai, some culture, etc.
I started tutoring Japanese about 2 years after I started studying it. It’s what got me into teaching, actually.
If your student trusts you enough to teach it to them, I’d say go for it!