My MacBook Pro is from 2009. Can I download the latest operating system?

No. OSX 10.11.6 is the latest you can run.

First, you should have created your own post since this one is about a 2009 MBP, not a 2011 iMac. Second it's already solved. But since you're here…

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How to upgrade to macOS High Sierra - Apple Support

I have a mid 2011 iMac and can't seem to upgrade beyond 10.11.6

If I can't upgrade, does it mean I need a new machine? it works fine otherwise (but virus protection etc needs later os)

many thanks

If I had the first idea how to start a new post...

Thanks for such speedy reply

cheers

You're welcome.

To start a new post, just type into the "Search or ask a question" field and it will bring up a list of similar questions and an "Ask the community" button. Click the button. :)