...C++14 is supported since gcc 5 and this one was released five years ago. I think it is reasonable to require a compiler from 2015...
I believe Scintilla is using C++17 features, so probably more like 2016-2018 for GCC, depending on which features Scintilla uses.
Sorry the misinformation. I refered to the note on the website. But yes, as @elextr said, the release announcements clearly state C++17. Even if gcc 7.3 from 2018 not as long ago as gcc 5, the other arguments are still true: the longer we wait, the harder the migration will be.