I had a guy come back to flying after 15 years recently and he only needed 10 hours to get up to speed and pass a skills test.
Having done a few check rides I find this interesting and something I have wrestled with. I have asked the question before how long does it take for the average person to become rusty.
Personally I reached the following conclusions:
1. It varies really quite significantly between individuals, but in general the more flying they have done the longer period of lapse they can have. On the whole someone with 500+ hours is significantly better than someone with 200 hours. There are some common denominators. It is evident those who were well trained in the first place. It is evident those who have flown a few different types.
2. For someone with 500+ hours if they have had three months off flying, in fact the 28 day rule or whatever it is many clubs impose is nonesense. After three months there is hardly any detectable loss of skill,
3. Between 3 and 6 months for the high hour pilot there is some degree of skill loss,
4. Instrument skills go much more quickly, and, the more complex the aircraft, the more likely the pilot is to struggle with some situations,
5. Much responsibility actually remains with the pilot. In some respects a circuit or two only proves (usually in benign conditions) the pilot can pull off a reasonable landing and handle the aircraft without immediate risk. However, it says nothing about his skills to deal with more difficult approaches, more challenging flying or an in flight emergency. For those reasons a check flight is often paying little more than lip serivce to currency. A pilot who, having been checked out, sets off on a long flight in poor weather with a new and more challenging approach at one end, and is unlucky enought to have to deal with an in flight "situation" may well find he is stretched to or beyond his limits, whereas the guy who has been flying regularly is more likely to be able to cope.