Is it acceptable to say "join" club activities?
Joining a club may even help you choose a career when you grow up. Some students are not sure what their interests are until they join club activities.
In the above context, it it acceptable?
That use is very normal in the US.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.