In Australia, you are generally not allowed to take a skateboard on a plane as carry-on luggage. Skateboards are mostly considered sporting equipment and must be checked-in.
Jetstar will allow you to carry on a skateboard as long as the "size, weight and item allowances are met."
Note that some airports do not allow skateboards and scooters (including electronic variations) to be taken through security checkpoints.
It's always a good idea to check with your specific airline to confirm their policies regarding skateboards, as some airlines and airports may have different rules or restrictions.