Paris greeter

Yes, I booked a tour with them 4 years ago. I was also solo and it was fine. My guide was male, retired and about my age. He spoke excellent English. We did a 3-hour walking tour of the Marais, which was very interesting and he pointed out a lot of things I wouldn't have found by myself. We met at Place des Vosges. I don't think you have any cause to be anxious.

I've used Paris Greeters a couple of years ago. My guide was a female in her early 40s. She showed me around Bastille for about 3 hours. My guide spoke great English and showed me tons of small, pretty courtyards in the area. I most likely would have missed those, if she would not have shown me.

I used Paris Greeters for our first trip to Paris. My greeter was an older woman. She took us on a tour of the Canal St Martin area. She showed us so many things we would have completely missed. I would not hesitate to use them again.

I have used Paris Greeters twice. Once the guide was female, once was male.
I felt very safe.
I would ask, though, that you not think of the service as a "free local guide," but more like seeing a neighborhood with a friend. The organization does request a donation on their web page, but that is voluntary. The guides won't accept tips but maybe a coffee or gelato. They aren't licensed and so cannot have a group of more than 5 or 6, but in both of my times with them it was only me and a friend.
For a more professional tour, Paris Walks offers guided tours of specific neighborhoods to larger groups for only 15 Euros. I have done 3 of those and recommend them as well.
Enjoy your time in Paris, my favorite city!

Thank you all for the very useful feedback, I felt a lot more confident and less anxious now. Thank you SharYn for your kindly reminder of who the greeters are, a cup of coffee in a great idea

We loved our Paris greeter. She was a retired doctor who wanted to practice her English. It was a great way to connect with a local Parisian!

Yes, I've used them. I expressed an interest in Architecture and had a tour from a retired Parisien architect. He gave me a choice between seeing the main area or seeing an area most people don't visit. I chose the latter. I learned a ton and the man was very nice and completely professional.