Correct, the requirements for Mojave is a 2012 or newer iMac. Your machine can go up to High Sierra but no further. Your are now 2 versions behind (as is my 2009 iMac) and in another release or two, you'll find that applications will begin to want Mojave as the minimum OS and you might have to upgrade to a newer Mac.
I know its quite old now nearly ten years
i dont use it very much as i use my macbook
air for daily things bank email etc.
And nearly all my internet is on my iPad.
But i might buy a newer macbook pro used.