can't update my macbook to any version later than 10.7.5 My Macbook is 1.8 GHZ Intel core 2 DUO with 2 GB DDR2 SDRAM, version 10.7.5.  I'm not sure what year I got it but it's old. 

I'm not able to perform an update to the most current version and I don't know why.

The reason I want to upgrade is that apps will not let me do an install on this OS version.  I tried installing a different OS, like Linux or Windows, but it did not go well.

It runs really well so I'm wondering if it has reached its end.
There are several resources for determining if your system will take 10.8 or newer. I did a search for "minimum system requirements for 10.8" and found plenty of sources stating that your 1.8GHz Core 2 Duo powered MacBook missed the mark. So did my MacPro1,1. 
This does not mean your system has reached its end. It'll still run fine with 10.6 or 10.7.