To put a different slant on it, compare flying with driving a car!!
When is someone an experienced driver??
This is normally measured in years of driving. We all know how easy it is to drive a car and how often we do it.
I would estimate that someone has to be driving about 5-6 years plus before they are considered experienced and thats for only driving a car.
So what about flying a plane, which is clearly a much more complex and dangerous affair?? I would suggest it is perhaps a combination of hours, currency, experience of flying different a/c into various airfields (not always the local strip) and airspace.
Happy landings, Mupp....