I don't think it's inappropriate to add people you meet on Facebook in your late 30's. Don't miss out on a chance to become friends with someone just because you think FB adding is a faux pas!
Also, where else would you post an event details page aside from Facebook? Meetup? That's even more dead..
It's more like, when you are in university it's fine to add other students you barely know. But now with a job, I don't want to add my colleagues or business associates to social media. Also real friends != FB friends, I'm not going to miss out on making personal connections because of this.
I dunno, I guess for events FB is still the place to go.
Also, where else would you post an event details page aside from Facebook? Meetup? That's even more dead..