While I definitely think you need to know how to sail before shoving off without a motor in a decent sized boat, there are some other considerations that might affect the level of competency needed, such as...
1. Where you are sailing, a lake? a calm bay with minimal tides? a river that can run 2 - 3 knots of current all day?
2. How busy is the area, what are the docks like? Just a few boats around and big long docks to pull into will make it easier, crowds and close quarters will be MUCH harder.
3. Do you have to be home for dinner, or can you end up anchored out for the night if winds and tides gang up on you?
I do know there are a number of people who sail in the Puget Sound engine-less, which is known for tough tides, but I am not yet one of them (although I want to be someday) Our boat is in the Columbia river now, and with the high currents nearly all the time, I do not think it would be feasible at all unless you do not mind anchoring for many hours, waiting for the small time when the currents drop to beat up the river.
1964 Islander 32
Saint Helens, OR