What do you mean by strike?

As in baseball -- "3 strikes ends your turn at bat."

What does that Perl being a mature platform mean?

It means that people build applications in Perl (as in C), and expect to only very rarely have to change them. Computing works because of mature platforms. If chip-makers decided on a whim to use ternary logic, or Intel to adopt an entirely new instruction set, or the C committee to call Ada95 "C2012" (and the GCC and Clang and MSVC maintainers agreed (there's only one Perl)) we'd all be hosed. Fortunately, they don't, so C, x86, and binary data storage are "mature platforms."