Among the major Facebook age segments, the fastest growing are teens (13-17) and young (26-34) to middle-age (35-44) professionals, with the growth in teens driven by non-U.S. markets. Also note the strong growth in the much smaller 45-54 and 55-59 age groups
So, social networking is not a teen thing anymore (if it ever was). Unfortunately, no numbers for Germany are mentioned in the article, so I took a quick look at Facebook myself and the result is the following:
So, while I have no earlier numbers to compare with, in contrast to the US, France and Turkey, the 18-28 age group in Germany is clearly below 50%. Additionally, the 13-17 age group is weaker than in the US or France, where it encompasses more than 15%. The German age distribution resembles the UK the most.
If you break it down in single years, you get the following distribution. The largest age class is 25. The high number for 65 probably should be an artifact.