My experience is much like that of Westernmeadowlark and custardcream. I have never noticed if I'm being noticed. My friends would be exasperated with me, my mother laughed, because even quite obvious attention especially male attention went completely over my head. I was never without a boyfriend though and men have told me "you're hard work, lovely but aloof" and "I thought you were out of my league"
As for Selfridges it's awful. I have a lovely glamorous beautiful friend who is very stylish and dripping in labels, even she gets snubbed. She's 33 and she spends money as a hobby.
I, on the other hand wear no flashy obvious labels, often vintage always black and quite alternative, 10 years older and I'm batting these sales people off.
I think with me it's my voice, I sound (I hate to say it) posh, she is not English. She was being ignored. I had Chanel running about opening all the drawers bringing out bags. I dislike their bags and took the mickey, and poked fun at the shoes, but they still insisted that " maybe this one will be more you"
I dislike shopping though, my idea of shopping is to go, in walk straight to the desk and ask for what I'm looking for.
As for invisible with age, I don't know on a personal level but it seems to be a thing. But to lament lack of attention seems shallow. Instead I think we women should celebrate our achievements and draw attention away from just our looks.