I'll never forget our first time swapping. We were only 18 and they were in their mid 30's. And we had no idea the other wife was bi and I was even more surprised when my wife started having sex with her.
It can be a bit intimidating for a first time couple. But my experience has been, if the more experienced couple is chill and takes it slow, it works. Once the nubbies decide to join, the passion takes over, and the sex is very exciting.