Well it depends if they 25+ and still in education then its perfectly fine, but if they not in education and started there working life It would be a bit weird to still be on here, unless your e.g. a nurse who's here to help guide future nurse students.....
I personally would not want to be on here once I started my career.
Postgraduate students, people who started university late, people who are looking for advice regarding "graduate" or "entry-level" positions, people looking to pass down relevant information e.g. teachers etc.
I'm 26 and still here. Haven't been a student for over a year now. Come at me.
In all seriousness I went through a long phase of not logging in when I started working, I just come on here when I'm bored or want some basic advice. It's easier than creating a new account on reddit or something. I try and input into educational stuff too to do with uni/course choice. There's loads of graduates on here.
they have finished education, this forum is liberal and boring for the most part, so why are they here?
Have you considered that people over 25 might still have something useful to add to the forum? That perhaps their collective wisdom and experience is valuable?