Australia- Long service leave entitlements questions?

If he is a true casual employee then he is not eligible for long service leave - that is something only for FT perm or contract employees. As a casual employee he would have been paid a small % extra on his salary since he started and this is to make up for things like LSL. You need to look at the contract he signed 11 years ago - this is where the LSL (if any) would be listed and when he could take it up. If he has taken any leave outside of annual leave then he may no longer be considered to have worked 11 years at the same job - it has to be continuous.