How can you control old system logs keep(or storage) time in Solaris ? Is there any method ? it depends on buffer size long or date long ?
It matters what version of Solaris you are running - anything newer than Solaris 8 should have a couple of log checkers running from root's cron.
Look for logchecker and newsyslog. These two will look at cron's log, messages file, syslog output.
You can figure out how much (by date/week) by looking at how often each runs.