Am I able to upgrade my Mac to macOS Catalina?

MacTracker turns up three models that match "imac14". Two are 21.5" models:

• 21.5" Late 2013 (iMac14,1 or iMac14,3) – Can run the latest version of Catalina, but nothing higher.
• 21.5" Mid 2014 (iMac14,4) – Can run the latest version of Big Sur, but nothing higher.

To determine which of these you have, select About This Mac in the Apple () menu and look at the model year / time of year in the model name.

I'm not sure what version of the operating system you mean by "X". Apple used the term "Mac OS X" for all of the operating systems from Mac OS X 10.0 ("Cheetah") through Mac OS X 10.11 ("El Captain"). They kept using "10.*" version names up through macOS 10.5 ("Catalina").

The iMacs in question shipped with assorted versions of Mountain Lion and Mavericks. Those are pretty old and if you are still using them, it is possible that you might have trouble using the App Store links to upgrade your Mac to Catalina or Big Sur. If you are in this boat and you do run into that sort of trouble, you might want to do the update in two steps – first upgrading to Sierra (the highest version of the OS available in the form of a simple .DMG), then using the versions of Safari and the App Store in Sierra to upgrade to the desired OS.

Very important note, Catalina does not support 32 bit software, if you depend on 32 bit software, keeping a Mojave copy on another partition handy is very helpful.

Upgrading to Mojave (Mac OS 10.14) - Apple Community

How to download and install macOS - Apple Support contains the system requirements and instructions.