I don’t think that data privacy laws would allow this, i.e. you can’t publicly broadcast someone’s age without their approval.
When racing, you will be able to see what category other riders are in.
Plus, what does it matter how old someone is? I’m 51 and a much stronger rider now than I was when I was 40, or even 30 to be honest. But i was only messing around on mountain bikes in those days.