My female pancake is 5.5 inches but I have only had her a few weeks, she laid 2 eggs for me 10 days ago!!
(She could have produced eggs previously to coming here so not sure what size she would have been then.)
Her weight is 431g
The male is certainly paying attention to her since she laid the eggs.
I'm not sure my female is actually just under 5.5 inches(similar to yours)-not sure if there is a specific safe size to be honest.
( still can't believe my female had two enormous eggs!)
Maybe someone else will comment on this-I personally wouldn't be worried and would put them together as they can be variable mature weights and sizes in nature.
You should be fine. She wont develop eggs without follicles. So if she not mature enough egg development wont occur. More than likely at that size she can lay an egg. Egg bound typically occurs from a variety of other issues. IE not a safe place to nest, stress, etc.. However i do recommend a quarantine period before placement with your male. Especially if this is a new acquisition and imported animal. Nothing wrong with WC just better safe than sorry. Oh and wheres the pics ?
I had fecal done, no parasites and here they are. He introduced himself by biting her head a few times and then falling asleep on her like this. There was no damage from his hello and there are 3 hide spots in the tank if she wants to hide.