Worstgen
Blackbeard
Pre-reveal of Bonney's age: Before the revelation that Bonney uses her Devil Fruit ability to alter her age, Blackbeard likely perceived her based on her appearance. During their early encounters, Bonney typically uses her power to make herself look like an adult woman. Therefore, Blackbeard might have believed her to be an adult, despite her actual younger age.
Blackbeard
After the revelation: Once Bonney's age manipulation ability is revealed, it becomes unclear if Blackbeard ever learned her true age. The manga doesn't explicitly show them interacting after this knowledge comes to light. Even if Blackbeard learned about the ability, it's still possible he wouldn't know Bonney's true age unless she chose to reveal it or accidentally reverted to her child form in his presence.
Blackbeard
Additional factors:
Blackbeard's personality: Given Blackbeard's generally pragmatic and self-serving nature, his interest in knowing Bonney's true age might have been limited. He'd likely be more concerned with her abilities and potential usefulness than her exact age.
Blackbeard's personality: Given Blackbeard's generally pragmatic and self-serving nature, his interest in knowing Bonney's true age might have been limited. He'd likely be more concerned with her abilities and potential usefulness than her exact age.