Will Pages/Keynote/Numbers (ex. iWork) be free for old macs?
It appears that everyone that owns an older copy of iWork for iOS gets a free upgrade whether or not your version came from a retail CD or the Mac App Store.
If you don't already own iWork - you will have to pay for either a new Mac or the apps piecemeal on the App Store.
The above summary is my understanding of this MacWorld article that includes calls with Apple Press relations and an "on-the-record" confirmation that all owners of iWork should get free upgrades despite some glitches in the initial roll out today.
In addition to upgrades for users of existing/previous installs of iWork, it has been shown that the logic that handles identifying whether you are eligible for an upgrade does not take into account whther your install was a trial or retail edition. In some cases, users with a trial version installed have found that upgrades were provided. It should be noted that the trial versions are no longer available for download officially.
No. It can be downloaded for free only for Macs purchased on or after October 1, 2013 (source).