Speaking from personal experience:
I am an overy forty trainee who recently who just took two months off and just got back to training two weeks ago- I noticed about a 25 to 30% decrease in raw strength and a marked decrease in endurance. My post work out aches and pains seem to be lasting longer. I am sure (hope)that this will all get back to " normal" after a few weeks of regular training.
When a person reaches beyond the limits of their ability; they shall they make progress. There is no other way.