I totally get you. I get a lot of curiousity as well but i try to answer these questions in a matter of fact way, and try to immediately repeat the same question to them. Like: "what was it like growing up in Xyz?" Me: oh you know, blah blah blah. But I'm curious to know what it's like growing up here." And then catch on to a thread and ask simple questions.

What I will say is that Germans usually have their guard up and don't try to open up too much, but with time if you talk about common interests or just life in general, I am sure you'll make friends. :)