I am a new BP breeder, I have a lot of questions & really would love to talk!

[PitOnTheProwl]

Anyway, given Frederick's age, is he sexually mature?.

In a word, yes. I have seen males as young as 6 months breed, weight is the big factor.

Frederick is a proven male, I tested this myself, but I just checked for sperm plugs and I can't tell if it was pee or sperm.

You have bred him before? Being proven and being a male are two different things.