I am taking my adult son (he'll be a week shy of 25 when we return) on the Italy / Switzerland trip this summer. We also did the Central Europe trip a few years ago. We very much enjoyed the company of everyone in the
ABD group as I hope we will this year.
With respect to African safaris, there are SO many companies to choose from depending on your budget. One that sounds very intriguing (but doesn't fit our schedule) is
National Geographic. Tauck Bridges also has a few good options as does Thomson Family Safaris. AMA does river cruises blended with safaris (even one that visits Victoria's Falls and S. Africa). When it comes to safaris you can really suffer from information overload. If you go to the TA forum and search for Tanzania safaris they have compiled quite a large list of companies that specialize in safaris and have received several positive reviews.
For our trip I have pretty much narrowed it down to Abercrombie and Kent (I have been wanting to try them for a long time and they have a trip that fits our schedule very well) and a private safari by African Dream Safaris (who have been AMAZING to deal with so far). Now I just have to decide if we want to be by ourselves (and have my teenage daughter suffer from lack of company her own age as well as lack of social media lol) or be with a group that may not share our interests. Decisions, decisions...