Setting: URLM_MAX_LOG_AGE

  Maximum age (in seconds) for URLs in the log. Set to zero to disable
  age-based trimming. Any URLs older than this will be removed from the
  log whenever the log is trimmed. This happens:

  - At startup (unless urlm_log_trim_startup is OFF)
  - Every urlm_log_trim_interval seconds (if urlm_log_trim_interval
    is non-zero)
  - Any time a URL is captured
  - When /urlm_trim_log is run manually

  This means that old URLs persist in the log for up to urlm_log_trim_interval
  seconds past their expiration time; if this annoys you, decrease the
  urlm_log_trim_interval to reduce the problem.