Earlier quoted context omitted.
Not before mainstream software supports it. We had 64-bit with Alpha, MIPS, SPARC, but 64-bit x86 only happened when it could run 32-bit x86 code flawlessly and it only got mass adoption when Windows went 64-bit.
We only got Intel 64 bit CPUs once AMD got them first and people starting to buy them.
Intel came first with Itanium (June 2001: https://en.wikipedia.org/w/index.php?title=Itanium&oldid=775...), which clearly is a 64 bit CPU. The first x86-64 CPU by AMD got released in April 2003 (https://en.wikipedia.org/w/index.php?title=X86-64&oldid=7754...) and Intel's first x86-64 CPU came out June 2004 (https://en.wikipedia.org/w/index.php?title=X86-64&oldid=7754...).