It is possible to set the number of days jobs are visible:
http://www.veritas.com/docs/000025879
However, depending on how busy the environment is, I don't recommend keeping 'massive' numbers of jobs, it slows the activity monitor down. I can't define 'massive' as it depends on how pwerful your master servers is / how busy it is. Just be very aware that an increase in job history may induce problems.
The best option, is to set up a OpsCenter server (the basic product is free) and this is more than capable of keeping large numbers of jobs. This would need to be set up on a seperate server.
