Older lightroom versions for download

LR Classic 8 (the latest version) requires Mac OS 10.12 or later, and thus won't run on your 10.11.

LR Classic 7 and LR CC (2015) (v6) require Mac OS 10.11 or later and should run on your system. (Though they may run slowly, given how old your computer is in Mac years.) However, Adobe in its infinited wisdom recently restricted which old versions you could download, and it won't allow downloads of LR 7, just LR CC (2015) (v6).

So you should be able to sign up for a Lightroom Classic subscription and then from the Creative Cloud desktop app download LR CC (2015) (v6).  When you click Apps, you should see the option for LR CC (2015)(v6):

What version do you have a license for? 1, 2, 3, 4, 5, 6?

You can't download or install any of the CC versions other than the newest and one back.

If you are a subscriber then you need a newer computer.

Hi eddiealexis9,

Are you able to get to a previous version of Lightroom following the steps below?

• Open the Creative Cloud desktop app by clicking the Creative Cloud icon in your taskbar (Windows) or the Apple menu bar (Mac OS). If you aren’t automatically signed in, sign in using your Adobe ID and password.
  
• Scroll to the app you want to install.
  
• Click the arrow next to Install or Open. Then, click Manage.