Can't help you in the real world because I did online dating at the age of 48. I'm not into the bar scene & found it worked perfectly. Marital status is on the profile (single, separated, widowed) so that part was easy. I dated a bit, met my now husband & have been with him for 4 yrs. (married 2).
My exH was your age when I left him. He meets women at a local upscale bar that is known for single people our ages LOL. I guess he just strikes up conversations & doesn't outright ask if they are single. It just flows....he is currently on his 2nd LTR girlfriend
Of course people lie about anything & everything online & IRL so be prepared for that.
As far as sex, again it just flows - no "rules."
With the woman you are seeing, start with light hand touching & shoulder brushing & see how she responds.
Stop worrying & have fun!
A cool guy in his (almost) mid-50's with grown children is VERY attractive to many single women.