There are no hard and fast rules on when to promote. In part, it depends on whether you need more editors (and more associate editors-in-chief). Here are some indicators for you to consider:

  1. number of reviews (for a given journal, for all ISI journals, for the last year, overall)
  2. quality of reviews
  3. number of journals reviewing for
  4. number of withdrawals (overall time, for the past year, for this journal, for all ISI journals)
  5. number of non-responses to requests to review
  6. length of service to ISI
  7. length of time in current position (as an associate, full, or senior), but the most important consideration is:
  8. “Do you trust this individual to take the job of mentoring others seriously?”