MM Pamphobeteus petersi Sizes??

[Liquifin]

I know guessing sizes isn't a good thing since it may vary, but I'm just questioning in general. I just recently gotten a young male P. petersi around 4.5''-4.75'' for my adult 6'' P. petersi female. I plan to breed these later in the future, but has anyone seen actual sizes of MM for this species?? This is just so I can expect when he might be pen-ultimate. Sorry for the not-so-big question from someone like me but there's no breeding reports that I can find on this species besides the common pamphos in the hobby. Anyone own MM of this species or bred this species before that can help?

Here's my young male