This is the essence of Molvar's argument:
"In his ’62 book on page 145 under the chapter titled "The myth of Middle age, he asks the question "Have you spent all your years sitting down at a clerical or physically-easy job?"
On the next page it says starting from nothing, "it would not be many weeks before he could run 10 miles, even if he could not run at all when he started." So what is "not many weeks". It is about 5 weeks. We are not talking months here. Two pages later he goes on to say "You can soon learn to run 20 miles if you want to." Well, if it takes about 5 weeks to get to 10, then soon would be another 4-5 weeks. Add it up and you get 9 weeks. Lydiard did not say 9 weeks of course but if you read what he says it is about 9 weeks for a sedentary office worker to 20 mile runs."
Sorry, Mr. Molvar, he never said it like you want him to have said it.
Again, I'd say it takes as long as it takes.