Experience with one of the "Big 4" Accounting Firms

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I have a CPA license and have worked at the same small firm for about 4 years. I only have tax experience, no audit exerience. I have been considering moving a larger firm.

If you have worked in one of these firms, or perhaps had a close friend or spouse who worked there, do you know anything about:

  1. Typical number of hours during peak season (January-April, Sept-Oct)
  2. Number of hours during non-peak season
  3. General atmosphere: friendly/robotic/cutthroat/etc
  4. Would it make a huge difference to make such a switch in one’s early 30s rather than late 20s?

Any insight or information greatly appreciated.

Thank you