How can I find out how old my computer is

Why do you want to know how old it is. It is more important to know what its model and model year is. That is what determines which operating system(s) can be installed. And in some instances, the OS you have installed determines what apps may be installed or upgraded. In case you do not know, the information about your computer can be seen in the window that opens when you click on About This Computer under the Apple icon.

Please follow the instructions I provided, it will tell you the model year of the computer. You can also get more specific information about it by using http://www.everymac.com/.

Also, we have no idea what you are referring to as "private information", please be specific about what type of information you consider private.

hnkrmmr wrote:

My computer is 0S X ElCapitan. version 10.11.6 . Where is all my private information stored?

What private information? Your files and documents should be stored in your Profile folder, unless you manually store them elsewhere. In Finder go to Your Mac/Macintosh/Users/Your Name.

Beyond that, what exactly are you trying to determine or accomplish?

You can determine the model year by clicking the Apple symbol in the upper left of the display and then clicking About this Mac. ATM will tell you the model year.