My boy is now 5 months old and his ears are still very large and floppy, I have seen other staffs with ears like this but at a younger age, as he was a rescue dog I never saw his parents so unsure what they looked like. Is this a sign he might be cross? Or will he grow into his ears?

As you don't know his parentage nobody can answer that question, however he's probably still teething which can make their ears do weird things, leave it a couple of months and see.

Ok, thank you