https://goo.gl/Wf7WAt

Like what Atoli said, gotta play catch up. They nerfed a lot of the primals and dungeons so he should be to 60 in no time. You both can still play together.

Once he completes "Before the Dawn" he can go into HW. You can help him with main story dungeons and primals, run palace of the dead together.

I helped many of my low level friends hit 60 just by playing casually. Good luck and have fun!

(The above link is for when you hit sixty.)