Ksh93/AIX compatibility

Hi everyone !

Im trying to know from wich version of AIX KSH93 is available ?
Internet tell me 6.x and 7.x AIX are available, bue what about 5.x ?
Is KSH93 available on AIX 5.x ?
Is it the same way to manipulate variables as KSH93 on 7.x ?

Thanks for your support and have a nice day !