As Lord Denning said in Roe -v- MoH [1954] one "must not look at the 1947 accident with 1954 spectacles". The standards that might have been expected in the late 60s and early 70s are not those of today and there are two distinctions to be drawn.

First - age, or rather sexual development. It has already been pointed out above that an 8 year old is a different person from a 15 year old, and even the law recognises this - Sections 5 to 8 deal with offences against teh under 13s (12 and downward) but SSn 9-15 13 to 15 and SSn 16 to 14 the limited range that relate to 16 to 18.

Second - coercion or its absence. You can't simply draw a realistic line between invited and uninvited sexual advances, as otherwise the first invitation is always an uninvited advance.

The 60s were the years of the great sexual revolution - they did not legitimate sex with under 13s, but, to be frank, sex with under 16s was commonplace (and the law of "abuse of position of trust" did not yet exist and still does not apply to rock stars or DJs with whom groupies want sex). Equally they did not legitimate coercion or assault.