Hmmm......I was told by the RS company that teens are allowed (and was specifically told that this was the recommended age, not necessarily a mandate) on ALL Rick Steves tours. I have the email from them stating this. Not that I'm trying to pick an argument saying your friend was wrong...
On our tour, I was talking to one of our tourmates and she mentioned that on her RS tour last year, one of her tourmates was a lady in her late 40's with her two daughters, who were in their early 20's. She said that an older, retired gentleman on the tour wasted no time on the first night saying that these tours are built for people over 45 and that no one younger than that should be on any of the RS tours. She politely informed him that he was incorrect and that if he only wanted to tour with people his age, surely there were companies out there that cater to that and perhaps he should find one. I've also seen a couple of similar sentiments on other websites where his tours are discussed (TripAdvisor, etc). Some people don't want kids on their trips. That was a MAJOR concern for me, especially when I learned that she was the only kid. But our tour group, who was just awesome in general, could not have been any kinder to her. Most of them sought her out to talk about her day, her likes, etc. In every single photo of the whole group, she's nowhere near my hubby and me, because someone would always pull her to them.
One other thing the RS offices told me is that obviously during most of the year, kids don't go on the tours because of school schedules. Where I live, we got out of school the Friday before Memorial Day and most other schools were still in session at that time....our tour began on May 30 so it didn't necessarily surprise me that no other kids were with us.
The RS offices had no issues with my 12 year old being booked on our trip. The lady I conversed with actually encouraged it.