I feel like they used a 19 year old because it…

I feel like they used a 19 year old because its half of Dan’s age

Still gross.  And it’s less than half, actually.

And this is an example where the writers should maybe have reassessed the risk of whether their joke was tipping Dan over from seeming not merely gross, but actively predatory.

I mean, remember when Jonah was hitting on all of Catherine’s classmates in 2.06, and the show absolutely put us in their shoes to demonstrate how creepy he was being?  And the age difference there was ten years, maybe, at the most, not an entire person who can vote plus some change.  

I’ve been a waitress – at maybe a year or two older than this Meagan – and I remember when men pushing forty or older used to try it on… it was at best uncomfortable.  Now, maybe we’re supposed to believe that Dan is so handsome and so charming that he’s the one man in a billion who doesn’t come across terribly when trying to have sex with someone who’s little more than a child, but… I tend to doubt it.  I have met some very beautiful men in my life (though none quite as beautiful as Dan, I’ll be honest) and not one of them could pull that off – I really don’t think it’s possible.

And, remember, this is a choice – you can still make the point about Dan being sexually gross and careless of Amy’s feelings if the girl is 23 or 25 or something slightly less blatantly unequal.