Apple - Is there a way to get the date of the first boot of an old mac?

The closest answer to my problem could be:

ls -lt /private/var/db/ | tail -3

which shows for example:

drwx------ 8 root wheel 272 Apr 18 2009 krb5kdc
drwx------ 3 root wheel 102 Apr 18 2009 dhcpclient
-r-------- 1 root wheel 48 Jan 14 2009 SystemKey

Ignoring the date of the "SystemKey"-file.

The file /private/var/db/.AppleSetupDone is created on the first boot. I'd bet it doesn't get migrated over from an old mac if you choose that, so it might be a good place to start your search for a file stamp.

Any file can be changed later, but you have to go looking for this one.

AppleCare can also provide you details if you give them your serial number. They have manufacture date, sale date (sometimes inaccurate) and possibly if the user runs the "Mac Buddy" setup assistant and registers the Mac online during the first boot.