highest OS version iMac G4 can go ?

Hey there,

How high an mac OS can my old iMac go ?

I'm not even sure how to identify which model of iMac it is. The older white one with the long arm and round base. iMac 1.25 GHz PowerPC G4 (3.3) , OS 10.3.9. What year does it make it ?

thanks,
tnixer