Is it possible to have multi-android version in your android device? Similar to PC having multiple OS in which you can select during boot up. I was wondering, for the time being, is it possible to have two android version in a android device?

Example: A android device with both android 2.2 and 4.0 installed. During boot up, user can select which one they wish to choose.

So, suppose there is a Apps that cannot be run on android 4, I can just switch to android 2.2. Same goes as vice-versa - if an apps can only be run on android 4, I just switch to android 4.
There's an app called Boot Manager (paid | free) which will allow you to install multiple roms on your device.  You select the ROM you wish to use whilst in the main OS and the application modifies the boot mechanism to point at the specific ROM.  It's only available for some devices though, I know that Samsung phones are definitely supported.