I picked this up in Fopp's as a birthday present for a good friend (who could be described using the noun and at least one of the adjectives in the title); he kindly lent it back to me once he'd finished it. He thought it "somewhat incoherent", and I'd agree with him - possibly whilst removing his generous modifier.
The author posits the existence of a type of stylish older man who "sees age as no reason to stop having fun" and backs this assertion up with descriptions of some of his own acquaintances: "He's just found out about lyric sites on the internet [...] He's immaculate, in black western shirt with pearly buttons [...] Leatherjacketish. Curly greying hair [...] Little Feat is his favorite band" (pp1-14). This observation appears fairly uncontentious (if not blindingly obvious, given the well-documented rise of the grey pound, dad rock and fifty quid bloke - all of which get mentioned in here), but it doesn't really get developed in the book.
The idea of using private individuals as exemplars is somewhat shaky: if we don't know them, how can we attest to their grooviness? Matters aren't improved when the author gives one of them space for his (unwisely unedited) reminiscences of childhood: e.g., "Beggin' 'pennies for the Guy' from the people queuing outside the Odeon Cinema on London Road. Notice that the 'Gaity' on Scotty Road was a Picture House but the 'Odeon' was a Cinema!!!!" (sic, p44). He's on somewhat surer ground when he brings in public figures, and there are some attempts to look at connections to music, politics, drugs and sex ["There's no such thing as a Groovy Young Conservative. Yet." (p110) "So, what we learn here is that the political grounding of the fifties and sixties is a terrific aid to grooviness" (p145)] but it still feels like he's trying to nail a jelly to a wall when trying to define the characteristics of a Groovy Old Man.
In fact, the giveaway comes right at the end of the book, in a desperate appeal to the reader: "Come on, you've read the book, now play the game. Jack Nicholson, certainly. But he's a film star. And he's American. David Bailey...? That bloke in the chemist, you know, the one with the ears..." (p230). This sounds like an author who's realised that an idea which might have made an interesting short article has been stretched too thinly to cover the length of a book.
Some boo-boos: James Hannay on p65 should, I think, be Richard, if the reference is to John Buchan's hero; Acker Bilk's hit (p89) was 'Stranger on the Shore' (there was only one of them); and anyone who believes (p123) John Lennon (rather than George Harrison) to be the author of 'Taxman' surely has abandoned all hope of ever being thought (or feelin') groovy.