That’s the annoying thing about the charge. Is the claim that he had consensual sex and paid her, but she was under 17 so it was “sexual assault”, or is the claim that he actually assaulted her against her will?
If the former, he was stupid for believing she didn’t lie about her age, because we all know that some women lie, despite the whole “we have to believe women” thing.
On the other hand, if he can prove that there was no way for him to know her age, then he might get off easy on that charge, only to face a charge for illegal prostitution.
Because “sugar daddy” doesn’t mean hooking up with a girl and paying her for sex — that’s actual prostitution.
Ignorance is not a defense for sexual assault of the statutory type. He’s toast.
“Sugardaddy dot com” sounds like a cover for underage trafficking.