In my opinion, yeah under law its the others resposibility to check but at the same time if a 16 year old is mature enough emotionally and physically that they fool other people then you cant really blame the adult. Also the whole age of consent is to protect children and a lot of people forget that so the only reason they want them to go to jail is to punish this "evil". Someone who commits a crime isnt always a bad person. Also in cases where a 20 year old dates an 80 year old or something like that, you should be protecting the old and probably not totally mentally capable and not the 20 year old who is probably using the 80 year old. But of course if i use these arguments irl people just call me a pedo so yeah.

I mean I think it’s the adults responsibility to make due diligent efforts to check, but if the minor continues to lie, is it really on the adult anymore? Unless there were glaring red flags that a reasonable person could suspect, I don’t believe the adult can be held responsible.

I have no idea how the law handles this, but from my understanding, “mens rea” (guilty mind) is required to prove criminal wrongdoing. There would be no “mens rea” proof here since the adult had to have willful intent to commit a crime.

So, you're the kinda guy asking for ID on a first date?