At least for C++, it's older than C++11; a lot of us used for a long time the "C++0x" pseudo-standard (which is mostly the draft of what later became C++11; as the C++0x name indicates, it was originally intended to be finished before 2010), and on most C++ compilers headers and types from C99 were available even when compiling C++ code (excluding MSVC, which really dragged their feet in implementing C99, and which AFAIK to this day still hasn't fully implemented all mandatory C99 features).
I believe it was somewhat older as part of typical C and C++ implementations, but don’t get standardized for a while. A big part of the older C and C++ standards are about unifying and codifying things that implementations were already doing.