Latest AEM SDK is not running with java 8

I have to check whether my current project which is in AEM 6.5 (jdk 1.8) will work on AemAACs or not and have seen many documentations mentioning AEM As a Cloud supports Java 8 and 11 both. Then what is the reason for this error. Could anyone please explain? If java 11 is now mandatory for AemAACs then how can I run both AEM 6.5 and AEMAACs together if my project has dependency on java 8.
Thanks

