Son's friend's mother is really friendly with teens. Is this weird?

[Angel-fire]

My son Dan (17) has a friend called Hannah. He and she used to go to school together and are now at the same college. They go out together about two or three times a month, with another 4 or 5 of the friends (male and female - all 17 to 22.)

Nobody's mother is like Hannah's mother. She has about 10 to 15 of the students at college and their old school pals on twitter and facebook, and she talks to them and comments on their facebook posts - maybe once or twice in a day, up to 5 to 10 times a month... Not *very* often, but moderately often. She may go 4 days without saying anything, but then engages in conversation with one of the 18 year olds for half an hour or so.

All of them - including Dan think she is 'cool' and great to talk to, a great listener, and funny and smart, and she treats them as if they were her age and doesn't talk to them as if they're 'kids.' She is about 46, and doesn't work, as she is a stay at home mum. She did work til about 40, but ill health with a chronic illness made her have to leave.

She doesn't seem weird or anything, but I find it odd that she is so friendly with 17 to 22 year olds. She goes to concerts sometimes with her daughter too (she is 18) and she thinks it's great to go with her mum. She also goes shopping with her daughter, like 3 or 4 times a month, and they're arm in arm like close mates.

She doesn't go out with all the daughter's friends or anything, but does seem friendly with them on the internet, as if she thinks she is 21, and they all think she is 'great.'

Does this woman's behaviour seem weird to you? It does to me, and it irks me a bit that all the kids seem to think she is great. What is so great about being pally with kids when you're 46?! Nobody else I know chit-chats to young people like this.
In answer to ZOMG, I do not have a daughter.

And to the others: I am NOT jealous. I just think her behaviour is odd and she seems childish. I mean, what 46 year old goes to concerts with the 18 y.o. daughter?