19 year old guy talking to 14 year old female?

My boyfriendish (we're not official) is talking to a 14 year old. I've told him that I feel weird about it but he says that there's nothing going on because she's too young and a family friend.

I find this odd because:

1. When I was 14 I'd never talk to someone 5 years older than me, and as an 18 year old I'd never form any kind of friendship/relationship with someone so much younger than me. Family friend or not.

2. She flirts with him constantly. And example: today she went on about how great pole dancing is and such.

3. Tonight she blew up his phone after we'd gone to bed and went as far as calling to get his attention.

I'm not sure if he's reciprocating any of her obvious feelings, but I feel like this is an extremely unhealthy relationship.

Am I just being weird? Over reacting?