Hi Kim! Thanks for starting this thread, and to everyone else for your great comments.
I am much more invisible to the opposite sex now than even 3 years ago. I commented on this in Ironkurtin's thread. I am not, however, invisible to my boyfriend! Also, I'm not invisible to my co-workers or family, or YLF -- also important.
Where I have noticed the invisible feeling: at work dealing with the public when I'm not the only one around. If someone comes in and wants directions or advice, or wants to speak to a manager, they 99% of the time go to my boyfriend or brother -- because they are middle-aged males. If they are coming in to ask a favor, for example, they want to use our restaurant's customer-only bathroom (without any intention of dining or buying a cup of coffee), they are much more likely to ask a teenage bus girl or 20-something server for the key.
I don't feel invisible at retail. First of all, I try to treat anyone in service with the respect, patience and kindness/a smile. I work in customer service, I know how hard it can be -- you have to bite your tongue all day long. I feel I usually receive excellent service because I go into it with a good attitude.
Having said all of this none of this bothers me too much, I am still overall happier in my 50s than I was in my 20s, 30s and especially 40s (my own personal hell time -- failed marriage, job losses, health problems, etc. etc.).
One final thought:
My mother always told me you can use the invisible thing to your advantage because people will underestimate you. I try to remember this as I become more invisible with age LOL!