Earlier quoted context omitted.
I'm still using my MBA from mid 2013. It's a wonderful thing. Battery is "replace soon" but it's mostly plugged in. It's battered and bruised, but still fast enough. I've been debating a change for a while and figured at the start of the year I'd wait to see if they were going to ditch the bf keyboard if they release a new MBA. Super glad I waited, fingers crossed I get the same life out of the next one! Say what you…
I have a 2009 MacBook Pro (Core2Duo + 4GB of ram), I've added an SSD years ago, and it runs absolutely fine, I use it almost daily to browse the web. Even the battery still works(only for about an hour, but it does).
You might want to consider running Manjaro[0] or Haiku[1] instead (I've had great luck with both on older MacBooks [2,3]).
Nessus reports El Capitan as a "Critical" vulnerability due to lack of security updates:
According to its self-reported version number, the Unix operating system running on the remote host is no longer supported.
Lack of support implies that no new security patches for the product will be released by the vendor. As a result, it is likely to contain security vulnerabilities.
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Mac OS X 10.11.6 (intel) support ended.
Upgrade to Mac OS X 10.14 / 10.13 / 10.12.
[2] https://tinyapps.org/blog/201811010700_linux_for_2009_macboo...