I'm in my 50's now and grew up watching Grange Hill, I was about the same age the kids in the school, Tucker Jenkins, Benny etc, I first realised I was getting old when I started fancying the mothers taking the kids to school rather than the main cast.
Another sign of getting old was being called 'Mister' by kids in the street, that was strange.
The biggy is walking through town and seeing people handing out flyers to clubs and raves etc, there comes a time when they're dishing them out like confetti and they take one look at you and ignore you giving the flyer the person behind lol, then you know you're past it.