By default on AIX cron process use the file /etc/cronlog.conf to customize cronlog.
In this file you can easily rotate cron logfile.

To log information in directory /var/cronjobs, log file cron.out, size of 50k, total number of rotated files = 4, archive in /var/cronarch, archive files with compression, create the configuration file as follows:

[root@aix001] /root> cat  /etc/cronlog.conf
...
logfile=/var/cronjobs/cron.out 
  size=50K 
  rotate=4 
  archive=/var/cronarch
  compress