It's hard. I've seen your message on teenagers and its really unfortunate that he sent crude messages, and more unfortunate in a way that you have read them. But out of all of that, your DD came across as sensible, so you've done a good job with her.
I have 4 DDs, my eldest is 16. She's had boyfriends, and whilst I've met a couple of them when they've come round to the house etc, or when I've seen her in a big group of friends, but I'd never dream of 'vetting' them before she goes out with them. That, in my view, would be sending a clear message that I don't trust her to make a sensible decision. And if I give her the impression I think she's too silly to be trusted, that's when she'll start acting silly.
I trust my DD. I am sure she will make a few mistakes, she's already made some belters in her life. But ultimately she has a good heart, she has her head screwed on, and she knows she can call for help any time day or night, and I will rescue her.
If you meet this boy, what do you expect will happen? He won't say things to you along the lines you have read in the messages. He isn't going to discuss his roller coaster cock with his girlfriend's mum! So he'll be a polite, probably quite shy 14 year old kid. And nothing will be gained.
Put systems in place to make sure she's safe. She can go out with him to a public place for example - I'm a fan of group dates, restaurant or Starbucks dates, cinema dates... I wouldn't be happy with a first date to an empty house. I'd want to know where and when she's coming back. I'd offer to pick her up. She needs a charged phone and instructions that if she decides he's not for her, to call or text and you will bail her out.
Make sure she is as safe as can be, then give her space.
Teens are hard, because they're growing up.