How is C and C++ not mature? C has been around for over forty years, while C++ over thirty years ago. Both have literally hundreds of IDEs and libraries built for them, millions of programs written in the language and numerous platforms for compilation.
They are literally the definition of a mature programming language and you toss them out like they are not.
And what do you mean "non-standard features in compilers", if it's a feature in a popular, mature compiler, it's a damn standard isn't it?