The source tarballs for older SageMath versions are at
Compiling from source on macOS will require installing
Apple's "Command-Line Tools for Developers".
Command-line tools should be enough.
Suggested commands to build Sage:
make configure
./configure
make openssl
make -s V=0
Some SageMath functionality is improved when
extra software is available, e.g. imagemagick and
ffmpeg help make animations out of Sage graphics.
The html documentation will be built and can be
browsed locally at this local url:
file:///path/to/sagedir/local/share/doc/sage/html/en/installation
where /path/to/sagedir
should be replaced with
the actual full path to the Sage directory, which
depending on where Sage was installed could be
/Users/username/SageMath
or /opt/sagemath
or /Applications/SageMath
or whatever location
was chosen.
To compile the pdf documentation, a working
LaTeX installation is required, such as the one
provided by TeXLive or MacTeX, with babel
language files for various languages.
Sage installs its own Python and all the Python
libraries it needs. Extra Python packages can be
installed by running
sage --pip install something
and other extra software by running
sage -i something
Let us know what version of SageMath builds there.
Happy to recommend extra software depending on
particular area of math.
That OS is about 7 years old, so maybe it's not surprising. Have you tried one of the OS X 10.11 binaries? Have you tried building from scratch?
I am currently running Sage 5.6 on this system, which I was able to install from a DMG I archived on an even older system. But I should be able to run something newer, like version 6.9 which runs on Mac OS X 10.7.
I'm working from home and this is the system I have. I can't afford a new one and I can't upgrade it because I have other maths-related work that will break if I upgrade its Mac OS.
Whatever reason would there be to delete Sage versions from all of the mirrors? That's just cruel.