How often should audits take place?

As a new board member I asked our property manager for a copy of our most recent audit only to be told there wasn't one.

So my questions are:

1. How often would you recommend an audit occur? The bylaws do not establish any guidance on when one should occur other than to say it can be requested.

2. Isn't it odd that a community that has been around for more than 30 years has not had an audit?