To disclaim, I tried to have a MFM threesome a couple times. Got only a BJ the first time, and the second time we had to suddenly interrupt it.
This one was different. First, in this case I put an ad on a local contact website and waited for someone to contact me. It took two months but after a first contact mail, we phoned like 20 mins to talk about fantasies, describe ourselves, and further arrangements.
They were F45M46 ish. She was really busty, small (155) and a bit overweight (which added to her curves). The man was brown skinned, taller than me, and of the quiet type. She did almost all of the talking. We arranged to meed at a local bar (far from my home) and then see what happens. I skipped half a jazz concert to go early and meet them.
We chatted a bit. They were impressed that a total nerd and innocent looking 24ish boy is into that stuff. I told them how hard it was to actually meet people. We dance and she can feel my dick getting really hard. It is not that big but I have had compliments on my friend down there. So it is on, she wants me and we decide to go to a nice motel in their car.