We (myself and the wife) did a 3500km tour around France and Northern Spain early summer this year. Everyone kept asking how much training we would do / had done - but, we did a short tour the previous October, then got on our bikes again to cycle into Plymouth to get the ferry to Roscoff as the tour started. The first week was good training for the second week, the first two good training for the next two etc. By the time we got to the Pyrenees we were plenty fit enough! And we are not fit youngsters, so training is not actually needed at all.