To be uncomfortable with dd's friend

[latealready]

DD is 11 and in Y7. She has made friends with a girl in year 11 who is 16 and does the same sport as her out of school, a teacher apparently told dd this and suggested she should talk to her about it and they have now spent a few breaks together and been texting each over.
She's asked dd if she wants to go shopping with her tomorrow afternoon, DD asked DH who automatically said yes, he thinks we let her go out on her own or with Y7's we haven't met before so why wouldn't we let her go out with a 16 year old friend.

AIBU to feel uncomfortable with this? I'm trying to hold myself back from saying I don't think she should but it just seems weird that a 16 year old would want to spend time with an 11 year old even if they do the same sport.
DD has a 22 year old sister who she is best friends with and spends a lot of time with which I don't find weird.

Difficult one. I can understand your reservations. Yanbu

Depends on the sport perhaps? I'd definitely think it was the driving force here. If it wasn't a shared interest they'd probably have little in common. I think horse riding is an area this seems to happen in? The age gap at stables doesn't seem to matter as everyone there is very focussed on the shared love of horses/horse care?

I wouldn't find it wierd if they have a shared interest, but I would be having a quick chat with the 16 year old about keeping conversations 'age appropriate.

My DS is 13 and although he has friends of his own age, he is also good friends with a 7 year old, who lives opposite. They are like brothers and it's lovely. They play and watch football together. I DS fully understands about age appropriate conversations. I am waiting for the time to come when my DS thinks of himself as being too old or mature to bother with the 7 year old.

At the moment though, it's just lovely.

Maybe ask to meet her? It's possible that the older girl sees herself as a mentor for the sport and is trying to build up rapport.

Also is it a niche sport or is the older girl competing to a high level? The 16yr old may not have/or be interested in a group of peer friendships if she spends a lot of time on training, so she may be enjoying the friendship with your Dd without having to commit to a full on one iyswim. Or she might be looking at it as a bit of a mentoring role. Are you dropping Dd off if she goes? That way you can size up the situation yourself.

Take them both for coffee and cake first?