In 1982, my coworkers Tommy and Barbara dated.
What happened with them after they started dating?
One month later, they were having sex in Tommy's house 2 times a week
That is an odd thing to remember. Usually it is discouraged to date people in your office. I don't think it is good to bring up in normal conversation though especially if they aren't together.
Why wouldn't it be appropriate?
Because people find talking about sex life to be uncomfortable. You should bring up more mundane stuff instead.