Derek Taylor's book is called
As Time Goes By, a slim volume of about 150 pages, first published in 1973. I read it years ago and I must confess that I don't remember anything from it! Michael Braun's
Love Me Do is a first hand account of the Beatles' rise to international fame. Braun, a journalist, was part of the Beatles' entourage during the first American tour. The book appeared in 1964. The sense of wonder at what was happening is palpable and borders on disbelief, and although Braun tries to be as discreet as possible, his account is more revealing than many later books. A quick read and a historical document!
I think this is where we disagree. When they conquered Britain in 1963 all teenagers were fans, plus they conquered a lot of older people ...
Do we really disagree? When they conquered Britain, the Beatles were no longer teenagers, but their fans were. They won over older people as well, true, but that was at least partly due to their specific Britishness and does not necessarily apply elsewhere. In other parts of the world they became weapons in the hands of teenagers fighting their conservative parents. Remember all those discussions over 'the generation gap', about youth going to the dogs, of psychologists' warnings etcetera. It's even in the films: the gentleman with the bowler hat on the train (in A Hard Day's Night) who 'fought the war for the likes of you', on the one hand, and the middle-aged housewives in Help, on the other, who like them and wonder if it's proper to wave at them.
In Paris, the Beatles wonder why there was a majority of 14- or 15-year old boys in their audience. And look at the vast majority of teens in the Shea Stadium audience. But maybe you're right and any watershed that separates age groups among the Beatles' fans is more or less artificial.
Here's a link to one source about the controversy Emerick/Scott that Moogmodule and Zipp mentioned:
http://www.macca-central.com/news/2100/